Novel polypeptide hormone phosphatonin

ABSTRACT

The present invention relates to a novel human protein called phosphatonin, and isolated polynucleotides encoding this protein. Also provided are vectors, host cells, antibodies, and recombinant methods for producing this human protein. The invention further relates to diagnostic and therapeutic methods useful for diagnosing and treating disorders related to this novel human protein.

FIELD OF THE INVENTION

The present invention relates to a polypeptide which is involved in theregulation of phosphate metabolism. More specifically, the presentinvention relates to a novel polypeptide Metastatic-tumor ExcretedPhosphaturic-Element (MERE) or “phosphatonin”. This invention alsorelates to genes and polynucleotides encoding phosphatonin polypeptides,as well as vectors, host cells, antibodies directed to phosphatoninpolypeptides, and the recombinant methods for producing the same. Alsoprovided are diagnostic methods for detecting disorders relating tophosphate metabolism, and therapeutic methods for treating suchdisorders. The invention further relates to screening methods foridentifying agonists and antagonists of phosphatonin activity.

Several documents are cited throughout the text of this specification.Each of the documents cited herein (including any manufacturer'sspecifications, instructions, etc.) are hereby incorporated herein byreference; however, there is no admission that any document cited isindeed prior art as to the present invention.

BACKGROUND OF THE INVENTION

Phosphate plays a central role in many of the basic processes essentialto the cell and the mineralization of bone. In particular, skeletalmineralization is dependent on the regulation of phosphate and calciumin the body and any disturbances in phosphate-calcium homeostasis canhave severe repercussions on the integrity of bone. In the kidney,phosphate is lost passively into the glomerular filtrate and is activelyreabsorbed via a sodium (Na⁺) dependent phosphate cotransporter. In theintestine, phosphate is absorbed from foods. A sodium (Na+) dependentphosphate cotransporter was found to be expressed in the intestine andrecently cloned (Hilfiker, PNAS 95(24) (1998), 14564-14569). The liver,skin and kidney are involved in the conversion of vitamin D3 to itsactive metabolite, calcitriol, which plays an active role in themaintenance of phosphate balance and bone mineralization.

Vitamin D deficiency causes rickets in children and osteomalacia inadults. Both conditions are characterized by failure of calcification ofosteoid, which is the matrix of bone. There are also several non-dietaryconditions which can lead to rickets, including X-linked vitamin Dresistant hypophosphatemic rickets (HYP), hereditary hypercalciuria withhypophosphatemic rickets (HHRH), Dent's disease including certain typesof renal Fanconi syndrome, renal 1 alpha-hydroxylase deficiency (VDDRI), defects in 1,25-dihydroxy vitamin D3 receptor (end organ resistance,VDDR II), and oncogenic hypophosphatemic osteomalacia (OHO). Thus, anumber of familial diseases have been characterized that result indisorders of phosphate uptake, vitamin D metabolism and bonemineralization. Recently a gene has been cloned and characterized thatis defective in patients with X-linked hypophosphatemic rickets (PHEX)(Francis, Nat. Genet. 11 (1995), 130-136; Rowe, Hum. Genet. 97 (1996),345-352; Rowe, Hum. Mol. Genet. 6 (1997), 539-549). The PHEX gene is atype II glycoprotein and a member of a family (M13), of Znmetalloendopeptidases. PHEX is proposed to function by processing afactor that plays a role in phosphate homeostasis and skeletalmineralization (Rowe, Exp. Nephrol. 5 (1997), 355-363; Rowe, CurrentOpinion in Nephrology & Hypertension 7(4) (1998), 367-376). Oncogenichypophosphatemic osteomalacia (OHO), has many similarities to HYP withan overlapping pathophysiology, but different primary defects (Rowe,Exp. Nephrol. 5 (1997), 355-363; Rowe, Current Opinion in Nephrology &Hypertension 7(4) (1998), 367-376; Drezner in Primer on Metabolic BoneDiseases and Disorders of Mineral Metabolism (ed. Favus, M. J.) 184-188(Am. Soc. Bone and Min. Res., Kelseyville, Calif., 1990)). Osteomalaciais the adult equivalent of rickets, and a key feature of tumour-acquiredosteomalacia is softening of the bones. The softened bones becomedistorted, resulting in bow-legs and other associated changesreminiscent of familial rickets. Low serum phosphate, and abnormalvitamin D metabolism are also key features shared with HYP. Tumouracquired osteomalacia is rare, and the tumours are mainly of mesenchymalorigin, although a number of different tumour types have also beenreported (Rowe, Exp. Nephrol. 5 (1997), 355-363; Francis, BaillieresClinical Endocrinology and metabolism 11 (1997), 145-163; loakimidis,The J. Rheumatology 21(6) (1994), 1162-1164; Lyles, Ann. Intern. Med. 93(1980), 275-278; Rowe, Hum. Genet. 94 (1994), 457-467; Shane, Journal ofBone and Mineral Research 12 (1997), 1502-1511; Weidner, Cancer 59(1987), 1442-1442). Surgical removal of the tumour(s) when possible,results in the disappearance of disease symptoms and bone healing,suggesting the role of a circulating phosphaturic factor(s) in thepathogenesis of the disease. Also, hetero-transplantation of tumoursinto nude mice (Miyauchi, J. Clin. Endocrinol. Metab. 67 (1988), 46-53)infusion of saline extracts into rats and dogs (Aschinberg, J. Paediatr.91 (1977), 56-60; Popovtzer, Clin. Res. 29 (1981), 418A (Abstract)), andthe use of tumour conditioned medium (TCM), of human and animal renalcell lines all confirm that a circulating phosphaturic factor issecreted by these tumours.

Although the primary-defect in X-linked rickets is confirmed as amutated Zn metalloendopeptidase (PHEX), there is considerable evidencethat implicates a circulating phosphaturic factor(s) (Ecarot, J. BoneMiner: Res. 7 (1992), 215-220; Ecarot, J. Bone Miner. Res. 10 (1995),424-431; Morgan, Arch. Intern. Med. 134 (1974), 549-552; Nesbitt, J.Clin. Invest. 89 (1992), 1453-1459; Nesbitt, J. Bone. Miner. Res. 10(1995), 1327-1333; Nesbitt, Endocrinology 137 (1996), 943-948; Qiu,Genet. Res., Camb. 62 (1993), 39-43; Lajeunesse, Kidney Int. 50 (1996),1531-1538; Meyer, J. Bone. Miner. Res. 4(4) (1989), 523-532; Meyer, J.Bone. Miner. Res. 4 (1989), 493-500). The overlapping pathophysiology ofHYP and OHO raises the intriguing possibility that the tumour-factor maybe processed in normal subjects by the PHEX gene product. Also, it islikely that proteolytic processing by PHEX may act by either degradingthis undefined phosphaturic factor(s), or by activating aphosphate-conserving cascade (Carpenter, Pediatric Clinics of NorthAmerica 44 (1997), 443-466; Econs, Am. J. Physiol. 273 (1997),F489-F498; Glorieux, Arch. Pediatr. 4 (1997), 102s-105s; Grieff, CurrentOpinion in Nephrology & Hypertension 6 (1997), 15-19; Hanna, CurrentTherapy in Endocrinology & Metabolism 6 (1997), 533-540; Kumar, Nephrol.Dial. Transplant. 12 (1997), 11-13; Takeda, Ryoikibetsu Shokogun Shirizu(1997), 656-659). The cloning and characterization of thetumour-phosphaturic factor is thus prerequisite to establishing anylinks between tumour osteomalacia and familial X-linked rickets as wellas other disorders in the phosphate metabolism.

Rowe et a/(1996) have reported candidates 56 and 58 kDa protein (s)responsible for mediating renal defects in OHO (Rowe, Bone 18, (1996),159-169). A patient with OHO was treated by tumor removal and pre- andpost-operative antisera from the patient were used in a Western blottingidentification of tumor conditioned media proteins. Neither the tumorcells nor the antisera were ever made available to the public, however.

In a review in Exp. Nephrol. 5 (1997), 335-363, Rowe (1997) discussesthe above diseases and the role of the PHEX gene (previously known asthe PEX gene). The PHEX gene product has been identified as a zincmetalloproteinase. In disease states such as familial rickets, defectivePHEX results in uncleaved phosphatonin which would result in downregulation of the sodium dependent phosphate cotransporter and upregulation of renal mitochondrial 24-hydroxylase. However, nopurification of phosphatonin was reported by Rowe (1997). Thus, nosource material for phosphatonin was made available to the public.Moreover, purification, identification and characterization ofphosphatonin has not been possible.

Thus, there is a need for polypeptides that regulate phosphatemetabolism, since disturbances of such a regulation may be involved inhypo- and hyperphosphatemic diseases, including osteomalacia,particularly osteoporosis and renal failure. Furthermore, there is aneed for identifying and characterizing such polypeptides which may playa role in the detection, prevention and/or correction of such disordersand may be useful in diagnosing those disorders.

SUMMARY OF THE INVENTION

The present invention relates to novel phosphatonin polypeptides and theencoding polynucleotides of phosphatonin. Moreover, the presentinvention relates to vectors, host cells, antibodies, and recombinantmethods for producing the polypeptides and polynucleotides. Alsoprovided are diagnostic methods for detecting disorders related to thepolypeptides, and therapeutic methods for treating such disorders. Thepresent invention further relates to screening methods for identifyingbinding partners of phosphatonin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: FIG. 1(a) and (b) show respectively chromatograms with lowaffinity and high affinity protein-containing peaks from a concanavalinA column.

FIG. 2: Cation exchange chromatogram of fractions from the concanavalinA column.

FIG. 3: Computer prediction of hydrophilicity and hydrophobicity ofphosphatonin.

FIG. 4: Computer prediction of antigenicity of phosphatonin.

FIG. 5: Computer prediction of flexibility of phosphatonin.

FIG. 6: Computer prediction of surface probability of the secondarystructure of phosphatonin.

FIG. 7: Computer prediction of the secondary structure of phosphatonin.

FIG. 8: Complete cDNA sequence (SEQ ID NO: 1) and amino acid sequence(SEQ ID NO: 2) of the largest MERE clone isolated (pHO11.1). The fiveother clone isolated are encompassed by this larger clone and all cloneare in frame with the cloning vehicle pBSCPT SK II-. Primers used forPCR are highlighted, and the total number of residues are 430 and 1655bp respectively. The prokaryotic expression vector pCal-n-EK containedall in frame residues from MEPE residue V, to the MEPE stop codon (TAG),at 1291-93 bp. The single polyadenylation sequence AA{T/U}AAA is doubleunderlined. The region of shared localized homology with DMA-1, DSSP,and OPN is underlined in wavy line format (MEPE-motif C-terminus), RGDresidues are enclosed in an ellipsoid), glycosaminoglycan attachmentsite is boxed (complete line format), Tyrosine Kinase site is underlinedonce, and N-glycosylation motifs are boxed in dotted line format. For acomplete list of motifs including casein kinase II, protein kinase Cetc. please refer to prosite screen Table 1.

FIG. 9: GCG-peptide-structure secondary structure prediction for MEPE.The primary amino acid backbone is shown as the central line with curvesindicating regions of predicted turn. Hydrophilicity/hydrophobicityregions are represented as ellipsoids and diamonds respectively and theRGD motif is indicated. The N-glycosylation sites are represented asellipsoids on stalks (C-terminus), and alpha helix by undulating regionson the primary backbone.

FIG. 10: Bar graphs showing phosphate-uptake in the presence ofdiffering amounts of MEPE: A. 92 ng/ml, B. 300 ng/ml, C. 500 ng/ml, andD. 1000 ng/ml. Choline boxes refer to control Na- independent resultswith NaCI replaced with choline chloride. Error bars are SEM, and Pvalues for the difference between MEPE and control in C and D are<0.001. In experiment A (92 ng/ml) P<0.05, and in B (300 ng/ml P, 0.01).N values for A and B are 4, and for C and D 5 and 6 respectively. Anovafollowed by Newman-Keuls Multiple Comparison Test was used.

FIG. 11: Dose curve of MEPE administration and phosphate uptake with SEMerror bars.

FIG. 12: Sequence similarity analysis using ‘sim’ and Ilanviewmathematical and software tools (Duret, Comput. Appl. Biosci. 12 (1996),507-510). In each computation the gap open penalty was set to 12, andgap extension penalty 4. Comparison matrix for A was ‘PAM40’, andBLOSUM62 for B and C respectively (see Duret, Comput. Appl. Biosci. 12(1996), 507-510; Huang, Comput. Appl. Biosci. 8 (1992), 155-165; Huang,Comput. Appl. Biosci. (1990) 6, 373-381). The similarity score thresholdwas 70% in A, and 40% in B and C respectively. The highlighted blocksshown on each protein scheme represent sequence homologies of >80% in A,and >62% in B and C. Note that in MEPE versus DSSP (A), there are fivehomology blocks in DSSP of >80% sequence similarity to a single motif inMEPE (DSSESSDSGSSSES). A similar sequence homology is also apparent forDMA-1 and OPN versus MEPE (B and C) and the MEPE is a feature of allthree proteins.

FIG. 13: Dot matrix comparison of DSSP versus MEPE using Antheprotstatistical analysis (Deleague, G. Software for protein analysis:Antheroplot V2.5e. Microsoft group. (7 Passage du Vercours 69-367Vercors Lyon Cedex 07, 1997)). In (A) a lower stringency comparison witha window set to 13 is used as screen parameters and in (B) a widerwindow of 15 is used. The colors indicate unity matrix cores asindicated on the diagram. C-terminal residues of MEPE-motif have >80%sequence homology and the repeat nature of the motif is illustrated bythe striped pattern.

FIG. 14: p1BL21 and also p6XL1 recombinant plasmids containingphosphatonin fusion construct. Lacl: (lac promoter); LIC: (Ligationindependent cloning sequence); EK: Enterokinase cleavage site; Thrombin(thrombin target sequence); Amp: Ampicillin resistance: Cal peptide(calmodulin peptide sequence); Phosphatonin (phosphatonin codingsequence).

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In view of the need of diagnostic and therapeutic means for thetreatment of diseases related to disorders in the phosphate metabolismin the human body, the technical problem of the invention is to providemeans and methods for the modulation of phosphate metabolism which areparticularly useful for the treatment of bone mineral and renaldiseases.

The above-defined technical problem is solved by the present inventionby providing the embodiments characterized in the claims. Accordingly,in one aspect the present invention relates to an isolated polypeptidehaving phosphatonin activity.

Unless otherwise stated, the terms used herein are defined as describedin “A multilingual glossary of biotechnological terms: (IUPACRecommendations)”, Leuenberger, H.G.W., Nagel, B. and Kölbl, H. eds.(1995), Helvetica Chimica Acta, CH-4010 Basle, Switzerland, ISBN 3-906390-13-6. The following definitions are provided to facilitateunderstanding of certain terms used throughout this specification.

The terms “treatment”, “treating” and the like are used herein togenerally mean obtaining a desired pharmacological and/or physiologicaleffect. The effect may be prophylactic in terms of completely orpartially preventing a disease or symptom thereof and/or may betherapeutic in terms of partially or completely curing a disease and/oradverse effect attributed to the disease. The term “treatment” as usedherein covers any treatment of a disease in a mammal, particularly ahuman, and includes: (a) preventing the disease from occurring in asubject which may be predisposed to the disease but has not yet beendiagnosed as having it; (b) inhibiting the disease, i.e. arresting itsdevelopment; or (c) relieving the disease, i.e. causing regression ofthe disease. The present invention is directed towards treating patientswith medical conditions relating to a disorder of phosphate metabolism.Accordingly, a treatment of the invention would involve preventing,inhibiting or relieving any medical condition related to phosphatemetabolism disorders.

In the present invention, “isolated” refers to material removed from itsoriginal environment (e.g., the natural environment if it is naturallyoccurring), and thus is altered “by the hand of man” from its naturalstate. For example, an isolated polynucleotide could be part of a vectoror a composition of matter, or could be contained within a cell, andstill be “isolated” because that vector, composition of matter, orparticular cell is not the original environment of the polynucleotide.

The phosphatonin polypeptide isolated in accordance with the presentinvention typically has an approximate molecular weight of 53 to 60 kDa,more preferably 58-60 kDa, as measured on SDS-PAGE, particularly on a12.5% gel at pH 8.6 in TRIS-Glycine SDS buffer, see Example 1. Anapproximate molecular weight of 200 kDa may be measured onbis-tris-SDS-PAGE at pH 7 using a 4-12% gradient gel with MOPS runningbuffer. It is possible on such a gel also to see lower molecular weightbands of 53 to 60 kDa. The polypeptide is generally glycosylated, andpreferably comprises phosphatonin in substantially pure form.

Surprisingly, it has been found that the phosphatonin is obtainable,following purification according to the protocol given in Example 1 fromSaos-2 cells, which are available from the European Collection of CellCulture under Deposit No. ECACC 89050205. Accordingly, in a furtheraspect of the invention, there is provided use of Saos-2 cells or HTB-96cells for the production of phospatonin. Other transformed orimmortalized cell lines may be capable of overexpression ofphosphatonin, such as transformed osteoblast or bone cell lines.

The present invention also describes the characterization and cloning ofa gene that is a candidate for the above-described tumour-derivedphosphaturic factor and that is named phosphatonin or MEPE(Metastatic-tumour Excreted Phosphaturic-Element). To summarize,expression screening of a λZAPII-cDNA library constructed from mRNAextracted from an OHO tumour using antisera specific to tumorconditioned media (TCM) phosphaturic-factor was used. The protein isglycosylated and resolves as two bands on SDS-PAGE electrophoresis(58-60 kDa), with evidence of possible splicing or post translationalcleavage. The cloned cDNA codes for a protein of 430 residues (SEQ IDNO: 2) and 1655 bp in length (SEQ ID NO: 1). The entire 3′ end of thegene is present, with part of the 5′ end missing. The fusion proteincontaining 10 residues of P-galactosidase is highly potent at inhibitingNa+ dependent phosphate co-transport in a human renal cell line (CL8).Secondary structure prediction confirms that the protein is highlyhydrophilic with small localized regions of hydrophobicity and nocysteine residues. A number of helical regions are present, with twodistinct N-glycosylation motifs at the carboxy-terminus. A key featureis the presence of a cell attachment sequence in the same structuralcontext found in osteopontin. Proteolytic-sites adjacent to this motifmay result in altered receptor specificity for specific integrins asfound in osteopontin. Screening of the trembl database with MEPEsequence also demonstrated sequence homology with Dentin phosphoryn(DPP). In particular there is striking localized residue homology at theC′-terminus of MEPE with DPP, dentin-matrix protein-1 (DMA-1) andosteopontin (OPN). This region of MEPE contains a recurring series ofaspartate and serine residues (DDSSESSDSGSSSESD), with 80%, 65% and 62%homology with DSP, DMA-1 and OPN respectively. Moreover, when residuephysicochemical character is considered this homology rises to 93%,suggesting a shared or related biological-functionality. It is also ofnote that this structural motif overlaps a casein kinase IIphosphorylation motif in MEPE. Skeletal casein kinase II activity isdefective in rickets, and results in under phosphorylation ofosteopontin (Rifas, Calcif. Tissue Int. 61 (1997), 256-259). The caseinkinase II defect has thus been proposed to play a role in theunder-mineralization of bone matrix (Rifas, loc. cit.).

Dentin phosphoryn (DPP), is one part of a cleavage product derived fromdentin sialophosphoprotein (DSSP), with the other part known as dentinsialoprotein (DSP) (MacDougall, J. Biol. Chem. 272 (1997), 835-842). Itis of particular interest that DSSP, DMA-1, OPN and MEPE are RGDcontaining phospho-glycoproteins with distinct structural similaritiesand major roles in bone-tooth mineralization (Linde, Crit. Rev. OralBiol. Med. 4 (1993), 679-728).

The new OHO tumour-derived phosphaturic factor named phosphatonin orMEPE described in the present invention, effects bone mineralhomeostasis by regulating Na+ dependent phosphate co-transport, vitaminD metabolism, and bone mineralization.

As set out in further detail below, a polynucleotide has been isolatedwhich encodes polypeptides according to the present invention; seeExample 2. The amino acid and nucleotide sequences of phosphatonin areset out in FIG. 8 (SEQ ID NO: 1 and SEQ ID NO: 2, respectively).Accordingly, the polypeptide of the present invention comprises theamino acid sequence of FIG. 8, optionally including mutations ordeletions which do not substantially affect the activity thereof. Suchmutations include substitution of one or more amino acids, particularlyby homologues thereof, as well as additions of one or more amino acids,especially at the N or C termini. Deletions include deletions from the Nor C termini. Substitutions by both naturally-occurring and syntheticamino acids are possible. Also included are polypeptides modified bychemical modification or enzymatic modification. Further, fragmentpeptides, whether chemically synthesized or produced by a biologicalmethod, whether modified or unmodified, are included within the scope ofthis invention.

Accordingly the present invention relates to a phosphatonin polypeptideor an immunologically and/or biologically active fragment thereof, whichcomprises an amino acid sequence encodable by a polynucleotide selectedfrom the group consisting of

-   -   (a) polynucleotides encoding at least the mature form of the        polypeptide comprising the amino acid sequence depicted in SEQ        ID NO: 2 (FIG. 8);    -   (b) polynucleotides comprising the coding sequence as depicted        in SEQ ID NO: 1 (FIG. 8) encoding at least the mature form of        the polypeptide;    -   (c) polynucleotides encoding a polypeptide derived from the        polypeptide encoded by a polynucleotide of (a) or (b) by way of        substitution, deletion and/or addition of one or several amino        acids of the amino acid sequence encoded by the polynucleotide        of (a) or (b);    -   (d) polynucleotides comprising the complementary strand which        hybridizes with a polynucleotide of any one of (a) to (c);    -   (e) polynucleotides encoding a polypeptide the sequence of which        has an identity of 60% or more to the amino acid sequence of the        polypeptide encoded by a polynucleotide of any one of (a) to        (d);    -   (f) polynucleotides encoding a polypeptide capable of regulating        phosphate metabolism comprising a fragment or an epitope-bearing        portion of a polypeptide encoded by a polynucleotide of any one        of (a) to (e);    -   (g) polynucleotides encoding an epitope-bearing portion of a        phosphatonin polypeptide comprising amino acid residues from        about 1 to 40, 141 to 180 and/or 401 to 429 in SEQ ID NO: 2        (FIG. 8);    -   (h) polynucleotides comprising at least 15 nucleotides of a        polynucleotide of any one of (a) to (g) and encoding a        polypeptide capable of regulating phosphate metabolism;    -   (i) polynucleotides encoding a polypeptide capable of regulating        phosphate metabolism comprising the cell and/or        glycosaminoglycan attachment motif and/or the bone mineral motif        of a polypeptide encoded by a polynucleotide of any one of (a)        to (h); and    -   (j) polynucleotides the nucleotide sequence of which is        degenerate as a result of the genetic code to a nucleotide        sequence of a polynucleotide of any of (a) to (i).

As used herein, a phosphatonin “polynucleotide” refers to a moleculehaving a nucleic acid sequence contained in SEQ ID NO: 1 or encoding thephosphatonin polypeptide of the present invention. For example, thephosphatonin polynucleotide can contain the nucleotide sequence of thefull length cDNA sequence, including the 5′ and 3′ untranslatedsequences, the coding region, as well as fragments, epitopes, domains,and variants of the nucleic acid sequence.

Moreover, as used herein, a phosphatonin “polypeptide” refers to amolecule having the translated amino acid sequence generated from thepolynucleotide as broadly defined.

A phosphatonin “polynucleotide” also includes those polynucleotidescapable of hybridizing, under stringent hybridization conditions, tosequences contained in SEQ ID NO: 1 or the complement thereof.“Stringent hybridization conditions” refers to an overnight incubationat 42° C. in a solution comprising 50% formamide, 5×SSC (750 mM NaCl, 75mM sodium citrate), 50 mM sodium phosphate (pH 7.6), 5×Denhardt'ssolution, 10% dextran sulfate, and 20 μg/ml denatured, sheared salmonsperm DMA, followed by washing the filters in 0.1×SSC at about 65° C.Further suitable hybridization conditions are described in the examples.

Also contemplated are nucleic acid molecules that hybridize to thephosphatonin polynucleotides at lower stringency hybridizationconditions.

Changes in the stringency of hybridization and signal detection areprimarily accomplished through the manipulation of formamideconcentration (lower percentages of formamide result in loweredstringency); salt conditions, or temperature. For example, lowerstringency conditions include an overnight incubation at 37° C. in asolution comprising 6×SSPE (20×SSPE=3M NaCl; 0.2M NaH₂PO₄; 0.02M EDTA,pH 7.4), 0.5% SDS, 30% formamide, 100 μg/ml salmon sperm blocking DNA;followed by washes at 50° C. with 1×SSPE, 0.1% SDS. In addition, toachieve even lower stringency, washes performed following stringenthybridization can be done at higher salt concentrations (e.g. 5×SSC).

Note that variations in the above conditions may be accomplished throughthe inclusion and/or substitution of alternate blocking reagents used tosuppress background in hybridization experiments. Typical blockingreagents include Denhardt's reagent, BLOTTO, heparin, denatured salmonsperm DNA, and commercially available proprietary formulations. Theinclusion of specific blocking reagents may require modification of thehybridization conditions described above, due to problems withcompatibility. Of course, a polynucleotide which hybridizes only topolyA+ sequences (such as any 3′ terminal polyA+tract of a cDNA shown inthe sequence listing), or to a complementary stretch of T (or U)residues, would not be included in the definition of “polynucleotide,”since such a polynucleotide would hybridize to any nucleic acid moleculecontaining a poly (A) stretch or the complement thereof (e.g.,practically any double-stranded cDNA clone).

The phosphatonin polynucleotide can be composed of anypolyribonucleotide or polydeoxribonucleotide, which may be unmodifiedRNA or DMA or modified RNA or DMA. For example, phosphatoninpolynucleotides can be composed of single-and double-stranded DMA, DMAthat is a mixture of single- and double-stranded regions, single- anddouble-stranded RNA, and RNA that is mixture of single- anddouble-stranded regions, hybrid molecules comprising DNA and RNA thatmay be single-stranded or, more typically, double-stranded or a mixtureof single- and double-stranded regions. In addition, the phosphatoninpolynucleotides can be composed of triple-stranded regions comprisingRNA or DNA or both RNA and DNA. Phosphatonin polynucleotides may alsocontain one or more modified bases or DNA or RNA backbones modified forstability or for other reasons. “Modified” bases include, for example,tritylated bases and unusual bases such as inosine. A variety ofmodifications can be made to DNA and RNA; thus, “polynucleotide”embraces chemically, enzymatically, or metabolically modified forms.

Phosphatonin polypeptides can be composed of amino acids joined to eachother by peptide bonds or modified peptide bonds, i.e., peptideisosteres, and may contain amino acids other than the 20 gene-encodedamino acids. The phosphatonin polypeptides may be modified by eithernatural processes, such as posttranslational processing, or by chemicalmodification techniques which are well known in the art. Suchmodifications are well described in basic texts and in more detailedmonographs, as well as in a voluminous research literature.Modifications can occur anywhere in the phosphatonin polypeptide,including the peptide backbone, the amino acid side-chains and the aminoor carboxyl termini. It will be appreciated that the same type ofmodification may be present in the same or varying degrees at severalsites in a given phosphatonin polypeptide. Also, a given phosphatoninpolypeptide may contain many types of modifications. Phosphatoninpolypeptides may be branched, for example, as a result ofubiquitination, and they may be cyclic, with or without branching.Cyclic, branched, and branched cyclic phosphatonin polypeptides mayresult from posttranslation natural processes or may be made bysynthetic methods. Modifications include acetylation, acylation,ADP-ribosylation, amidation, covalent attachment of flavin, covalentattachment of a heme moiety, covalent attachment of a nucleotide ornucleotide derivative, covalent attachment of a lipid or lipidderivative, covalent attachment of phosphatidylinositol, cross-linking,cyclization, disulfide bond formation, demethylation, formation ofcovalent cross-links, formation of cysteine, formation of pyroglutamate,formulation, gamma-carboxylation, glycosylation, GPI anchor formation,hydroxylation, iodination, methylation, myristoylation, oxidation,pegylation, proteolytic processing, phosphorylation, prenylation,racemization, selenoylation, sulfation, transfer-RNA mediated additionof amino acids to proteins such as arginylation, and ubiquitination;see, for instance, PROTEINS -STRUCTURE AND MOLECULAR PROPERTIES, 2ndEd., T. E. Creighton, W. H. Freeman and Company, New York (1993);POST-TRANSLATIONAL COVALENT MODIFICATION OF PROTEINS, B. C. Johnson,Ed., Academic Press, New York (1983), pages. 1-12; Seifter, Meth.Enzymol. 182 (1990); 626-646, Rattan, Ann. N.Y. Acad. Sci. 663 (1992);48-62. For example, it is possible that phosphatonin is expressed as apreproprotein and after processing of the pre-sequence and optionallypro-sequence is cleaved into two or more fragments which remain togetherdue to the formation of, for example, hydrogen bonds. The processingand/or cleavage of the prepro- and even mature form of the phosphatoninpolypeptide may be accompanied by the loss of one or more amino acids atthe cleavage site. It is to be understood that all such forms of thephosphatonin protein are encompassed by the term “phosphatoninpolypeptide”, “polypeptide” or “protein”.

“SEQ ID NO: 1” refers to a phosphatonin polynucleotide sequence while“SEQ ID NO:2” refers to a phosphatonin polypeptide sequence.

A phosphatonin polypeptide “having biological activity” refers topolypeptides exhibiting activity similar, but not necessarily identicalto, an activity of a phosphatonin polypeptide as measured in aparticular biological assay such as described below, with or withoutdose dependency. In the case where dose dependency does exist, it neednot be identical to that of the phosphatonin polypeptide, but rathersubstantially similar to the dose-dependence in a given activity ascompared to the phosphatonin polypeptide (i.e., the candidatepolypeptide will exhibit greater activity or not more than about 25-foldless and, preferably, not more than about ten-fold less activity, andmost preferably, not more than about three-fold less activity relativeto the phosphatonin polypeptide). The term “immunologically active” or“immunological activity” refers to fragments, analogues and derivativesof the phosphatonin polypeptide of the invention the essentialcharacteristic immunological properties of which remain unaffected inkind, that is that the polynucleotides of the invention include allnucleotide sequences encoding proteins or peptides which have at least apart of the primary and/or secondary structural conformation for one ormore epitopes capable of reacting specifically with antibodies unique tophosphatonin proteins which are encodable by a polynucleotide as setforth above. Preferably, the peptides and proteins encoded by apolynucleotide of the invention are recognized by an antibody thatspecifically reacts with an epitope of the phosphatonin polypeptidecomprising the amino acid residues of about 20 to 30, 100 to 130, 145 to160, 300 to 310, 320 to 340 or 380 to 430 of SEQ ID NO: 2 or with anepitope of the phosphatonin polypeptides described herein below.Residues 380-430 peptides/antibodies are particularly useful for thestudy of mineralization processes, residues 145-160 peptides/antibodiesfor the study of receptor ligand interactions (inter gins etc.) andresidues 20-30 and 100-130, are of particular interest for phosphateregulations studies.

Preferably, the immunologically active phosphatonin peptide fragments,analogues and derivatives of the phosphatonin polypeptide of theinvention are capable of eliciting an immune response in a mammal,preferably in mouse or rat.

In a preferred embodiment of the present invention the phosphatoninpolypeptide is biologically active in that it is capable of regulatingor modulating phosphate metabolism, preferably it has “phosphatoninactivity”.

Phosphatonin activity

The term “capable of regulating or modulating phosphate metabolism” asused herein means that the presence or absence, i.e. the level of thephosphatonin polypeptide of the invention in a subject modulatesNa+-dependent phosphate co-transport, vitamin D metabolism and/or bonemineralization. Depending on whether the mentioned activities are up- ordown-regulated by the polypeptide of the invention, said “capability ofregulating or modulating phosphate metabolism” is referred to as“phosphatonin activity” and “anti-phosphatonin activity”, respectively.

Phosphatonin activity many be measured by routine assay, particularly asthe ability to down-regulate sodium dependent phosphate co-transportand/or up-regulate renal 25-hydroxy vitamin D3-24-hydroxylase and/ordown-regulate renal 25-hydroxy-D-1 a-hydroxylase. In each case,regulation of the relevant enzyme activity may be effected directly orindirectly by the phosphatonin; e.g., by measurement of radioactiveNa-dependent uptake of phosphate. These activities may be assayed usinga suitable renal cell line such as CL8 or OK (deposited at the EuropeanCollection of Cell Cultures under ECACC 91021202). A suitable assaymethodology is found in Rowe et al (1996). Phosphatonin activity mayfurther be measured by the ability to promote osteoblast-mediatedmineralization in tissue culture; see, e.g., Santibanez, Br. J. Cancer74 (1996), 418-422; Stringa, Bone 16 (1995), 663-670; Aronow, J. CellPhysiol. 143 (1990), 213-221; or as described in the appended examples.

In a further aspect, the present invention provides a polypeptidecomprising a bioactive fragment of the polypeptide described above.Without intending to be bound by theory, it is thought that phosphatoninmay function as a polyhormone which may be cleaved in vivo to form oneor more fragments at least some of which possess biological activitysuch as hormonal activity. In vivo it is thought that phosphatonin maybe cleaved proteolytically, for example by the PHEX gene product toproduce at least one functional fragment. In a preferred embodiment, thepolypeptide comprising the bioactive fragment is capable of regulatingphosphate metabolism, for example by possessing phosphatonin activity asdiscussed above, or by possessing the opposite of phosphatonin activityas discussed in further detail below. The bioactive fragment may be anN-terminal, C-terminal or internal fragment. The polypeptide comprisingthe bioactive fragment may further comprise additionally amino acidsequence provided that the activity of the bioactive fragment is notsubstantially affected.

Advantageously, the bioactive fragment has a cell attachment motif whichpreferably comprises RGD. As discussed in further detail below, thismotif may be involved in receptor and/or bone mineral matrixinteraction. Advantageously, the bioactive fragment has aglycosaminoglycan attachment motif, which preferably comprises SGDG (SEQID NO: 3). Attachment of glycosaminoglycan is thought to permit thefragment to resemble a proteoglycan. Proteoglycans are known to beinvolved in bone bioactivity, particularly in cell signaling. Thesemotifs are discussed in greater detail below.

In one embodiment of the present invention, the polypeptide comprisingthe bioactive fragment possesses phosphatonin activity. Withoutintending to be bound by theory, such activity is expected inphosphatonin uncleaved by PHEX metalloproteinase and some bioactivefragments carrying a PHEX metalloproteinase cleavage site such as thesite ADAVDVS (SEQ ID NO: 4) where cleavage is proposed to occur betweenresidues VD (residues 235 and 236). The bioactive fragment may compriseat least the first 236 residues of the amino acid sequence of FIG. 8 sothat this PHEX metalloproteinase cleavage site is part of the fragment.Such polypeptides and fragments thereof having phosphatonin activitywill be useful in treating hyperphosphatemic conditions.

Related proteins

Further studies carried out in accordance with the present inventionrevealed a number of distinct similarities between phosphatonin (MEPE),dentin matrix protein-1 (DMP1), dentin sialo phosphoprotein (DSSP; morespecifically the dentin phosphoryn C-terminus), bone sialoprotein (BSP)and osteopontin (OPN). In particular all the aforementioned matrixproteins have RGD motifs, are glycosylated with unusually high aspartateand serine contents. Casein kinase II phosphorylation motifs are acommon feature and there are localized regions of homology sharedbetween each of the proteins. Lanview-sim analyses Swissprot software(Duret, LALNVIEW: a graphical viewer for pairwise sequence alignments.Comput. Biosci. 12 (1996), 507-510) graphically illustrate the regionsof high homology as dot matrix comparisons between phosphatonin andDSSP. The motif is repeated five times in the dentin phosphoryn (DP)portion of DSSP (FIG. 12 a), and this motif has 80% homology to aC-terminal residue in phosphatonin. Based on physiochemical parameters a93% homology can be deduced and this sequence homologue is present inthe other bone/dentin molecules described with 60% to 65% sequencesimilarity. There is also in the same region extended sequence homologywith a run of residues between DMA-1 and phosphatonin as is shown inTable 2 and in the sequence comparison below: 408 SSRRRDDSSESSDSGSSSESDG429 MERE (SEQ ID NO: 5) 443 SSRSKEDSN-STESKSSSEEDG 463 DMA-1 (SEQ ID NO:6)

Dentin sialo-phosphoprotein (DSSP) is a large RGD-containingglycoprotein that in-vivo is cleaved to generate tow proteins known asdentin sialoprotein (DSP) and dentin phosphoryn (DP), respectively(MacDougall, J. Biol. Chem. 272 (1997), 853-842). DSP is the N-terminalpeptide and DP the C-terminal and both were originally thought to bederivatives of different genes. A statistical dot-matrix comparison ofphosphatonin versus DSSP at high and low stringency comparison is shownin FIG. 13. The repeat nature of the “motif-homologue” (DSSESSDSGSSSES(SEQ ID NO: 7)) in DSSP and its striking homology is clearly displayedin both graphical presentations. The motif is present only once in MEPEat the C-terminus. Moreover, overall low level sequence-similarity tothe C-terminal portion of DSSP (or the DP component) is clearlydisplayed. It is thus believed that a novel “unique” feature has nowbeen discovered that is likely to play a role in bone-mineralinteractions in bone-tooth matrix class of proteins.

In conclusion, all the proteins discussed appear to form integralassociations with bone mineral or tooth extracellular matrix and theinteractions are thought to be mediated via integrin/RGD associations.Moreover, the new regional motif (rich in serines and aspartate) wouldbe ideal for phosphate calcium interactions. This therefore supports thehypothesis that the C-terminus of phosphatonin plays a role in bonemineral homeostasis, and the N-terminus on renal phosphate regulation.In summary, the shared features of the proteins comprise:

1. RGD motif in similar structural context.

2. Glycoproteins.

3. Rich in aspartate and serine.

4. Casein kinase and protein kinase motifs.

5. Distinct aspartate-serine rich MERE motif (repeated in DPP).

6. Large number of phophorylation motif and myristoylation motifs.

7. Evidence of cleavage and/or alternative splicing.

8. All associated with bone or tooth extracellular matrix.

Thus, in a preferred embodiment of the present invention, thephosphatonin polypeptide comprises the above-described bone mineralmotif, preferably the amino acid sequence of SEQ ID NO: 5 or 7 or anamino acid sequence corresponding to the same such as those from thementioned DMP 1, DSSP, BSP, OPN or DMA-1 proteins.

Bioactive fragments

In another embodiment of the present invention, the polypeptidecomprising the bioactive fragment has the reverse of phosphatoninactivity and may be suitable for treating hypophosphatemic conditions.In this embodiment, the polypeptide is directly or indirectly capable ofup-regulating sodium dependent phosphate cotransport and/ordown-regulating 25-hydroxy vitamin D3-24-hydroxylase and/orup-regulating renal 25-hydroxy-D-1-hydroxylase. The mentioned activitieswill also be referred to herein as “anti-phosphatonin” activity.However, use of the term “anti-phosphatonin” activity does not excludethe possibility that said activity is the one which is predominant ofgenuine phosphatonin in phosphate metabolism. These “anti-phosphatonin”activities are also readily measurable using the methodology of Rowe etal (1996) by assay using a suitable renal cell line such as CL8 or OK(deposited at the European Collection of Cell Cultures under ECACC91021202); see also the methods referred to supra and in the appendedexamples. Thus, the phosphatonin polypeptides of the invention can beeasily tested for phosphatonin or “anti-phosphatonin” activity accordingto the methods referred to above or described further herein, e.g., inthe appended examples. Preferably, the fragment is obtainable byproteolytic cleavage of phosphatonin by a PHEX metallopeptidase. A PHEXgene has been cloned and found to encode a zinc metallopeptidase asdiscussed in Rowe (1997). Again, without intending to be bound bytheory, structurally, bioactive fragments having these activities arethought to lack at least a part of the N or C terminal portion of theamino acid sequence of FIG. 8, preferably lacking the C terminal portionup to at least the putative PHEX metalloproteinase cleavage site atresidues 235/236. This polypeptide therefore preferably comprises nomore than approximately the first 235 residues of the amino acidsequence of FIG. 8.

As is explained in Example 4, the phosphatonin polypeptide of theinvention was cloned via the use of an expression library, wherein thetarget cDNA is fused to a portion of the p-galactosidase enzyme. In thecDNAs so obtained the N-terminal methionine was not included. However,it is tempting to predict that genuine phosphatonin has an N-terminalmethionine present in its amino acid sequence. Therefore, in oneembodiment of the phosphatonin polypeptide of the invention the aminoacid sequence of the polypeptide includes the amino acid Met added tothe N-terminus.

In another embodiment, the polypeptide of the invention can be part of afusion protein. This embodiment will be discussed further below.

The present invention further provides a polynucleotide encoding aphosphatonin polypeptide as described herein. Such polynucleotide may bea DMA such as a cDNA, or an RNA such as mRNA or any other form ofnucleic acid including synthetic or modified derivatives and may encodethe polypeptide in a continuous sequence or in a number of sequencesinterrupted by intervening sequences. In which ever form it is present,the polynucleotide is an isolated polynucleotide in that it is removedfrom its naturally-occurring state. This aspect of the invention isbased on the cloning of the gene for human phosphatonin. In a preferredembodiment, the polynucleotide comprises the nucleotide sequence of FIG.8, optionally including one or more mutations or deletions which do notsubstantially affect the activity of the polypeptide encoded thereby.Such mutations include those arising from the degeneracy of the geneticcode, as well as those giving rise to any of the amino acid mutations ordeletions discussed above.

Accordingly, by the employment of techniques routine to those skilled inmolecular biology, it is possible to use the nucleotide sequence of FIG.8 to generate suitable polynucleotide sequences which encodepolypeptides useful in the present invention. As mentioned hereinbefore, the present invention also encompasses phosphatoninpolynucleotides, wherein the nucleotide sequence comprises sequentialnucleotide deletions from either the C-terminus or the N-terminus suchas those described in more detail below.

Extending the polvnucleotide sequence of the invention

As discussed in Example 4, the phosphatonin polynucleotide obtained bythe expression library may not be full-length at the 5′-end. Thepolynucleotide sequences encoding the phosphatonin polypeptides may thusbe extended utilizing partial nucleotide sequence and various methodsknown in the art to detect upstream sequences such as promoters andregulatory elements. Gobinda, (PCR Methods Applic. 2 (1993), 318-322)discloses “restriction-site” polymerase chain reaction (PCR) as a directmethod which uses universal primers to retrieve unknown sequenceadjacent to a known locus. First, genomic DMA is amplified in thepresence of primer to a linker sequence and a primer specific to theknown region. The amplified sequences are subjected to a second round ofPCR with the same linker primer and another specific primer internal tothe first one. Products of each round of PCR are transcribed with anappropriate RNA polymerase and sequenced using reverse transcriptase.

Inverse PCR can be used to amplify or extend sequences using divergentprimers based on a known region (Triglia, Nucleic Acids Res. 16 (1988),8186). The primers may be designed using OLIGO® 4.06 Primer AnalysisSoftware (1992; National Biosciences Inc, Plymouth Minn.), or anotherappropriate program to be preferably 22-30 nucleotides in length, tohave a GC content of preferably 50% or more, and to anneal to the targetsequence at temperatures preferably about 68°-72° C. The method usesseveral restriction enzymes to generate a suitable fragment in the knownregion of a gene. The fragment is then circularized by intramolecularligation and used as a PCR template.

Capture PCR (Lagerstrom, PCR Methods Applic. 1 (1991), 111-119) is amethod for PCR amplification of DNA fragments adjacent to a knownsequence in, e.g., human yeast artificial chromosome DNA. Capture PCRalso requires multiple restriction enzyme digestions and ligations toplace an engineered double-stranded sequence into an unknown portion ofthe DMA molecule before PCR. Another method which may be used toretrieve unknown sequences is that of Parker, (Nucleic Acids Res. 19(1991), 3055-3060). Additionally, one can use PCR, nested primers andPromoterFinder libraries to walk in genomic DNA (PromoterFindermClontech (Palo Alto Calif.). This process avoids the need to screenlibraries and is useful in finding intron/exon junctions. Preferredlibraries for screening for full length cDNAs are ones that have beensize-selected to include larger cDNAs. Also, random primed libraries arepreferred in that they will contain more sequences which contain the 5′and upstream regions of genes. A randomly primed library may beparticularly useful if an oligo d(T) library does not yield afull-length cDNA. Furthermore, direct sequencing of primer extensionproducts may be employed. Genomic libraries are useful for extensioninto the 5′ nontranslated regulatory region. Capillary electrophoresismay be used to analyze the size or confirm the nucleotide sequence ofsequencing or PCR products; see, e.g., Sambrook, supra. Systems forrapid sequencing are available from Perkin Elmer, Beckmann Instruments(Fullerton Calif.), and other companies.

Computer-assisted identification of phosphatonin polypeptides and theirencoding genes

BLAST2, which stands for Basic Local Alignment Search Tool (Altschul,Nucleic Acids Res. 25 (1997), 3389-3402; Altschul, J. Mol. Evol. 36(1993), 290-300; Altschul, J. Mol. Biol. 215 (1990), 403-410), can beused to search for local sequence alignments. BLAST produces alignmentsof both nucleotide and amino acid sequences to determine sequencesimilarity. Because of the local nature of the alignments, BLAST isespecially useful in determining exact matches or in identifyinghomologs. The fundamental unit of BLAST algorithm output is theHigh-scoring Segment Pair (HSP). An HSP consists of two sequencefragments of arbitrary but equal lengths whose alignment is locallymaximal and for which the alignment score meets or exceeds a thresholdor cutoff score set by the user. The BLAST approach is to look for HSPsbetween a query sequence and a database sequence, to evaluate thestatistical significance of any matches found, and to report only thosematches which satisfy the user-selected threshold of significance. Theparameter E establishes the statistically significant threshold forreporting database sequence matches. E is interpreted as the upper boundof the expected frequency of chance occurrence of an HSP (or set ofHSPs) within the context of the entire database search. Any databasesequence whose match satisfies E is reported in the program output.

Analogous computer techniques using BLAST (Altschul, 1997, 1993 and1990, supra) are used to search for identical or related molecules innucleotide databases such as GenBank or EMBL. This analysis is muchfaster than multiple membrane-based hybridizations. In addition, thesensitivity of the computer search can be modified to determine whetherany particular match is categorized as exact or homologous. The basis ofthe search is the product score which is defined as:

%sequence identity x % maximum BLAST score 100

and it takes into account both the degree of similarity between twosequences and the length of the sequence match. For example, with aproduct score of 40, the match will be exact within a 1-2% error; and at70, the match will be exact. Homologous molecules are usually identifiedby selecting those which show product scores between 15 and 40, althoughlower scores may identify related molecules.

Examples of the different possible applications of the phosphatoninpolynucleotides and polypeptides according to the invention as well asmolecules derived from them will be described in detail in thefollowing.

Phosphatonin Polynucleotides and Polypeptides

The phosphatonin was isolated from a cDNA library constructed from mRNAextracted from a meningeal phosphaturic-mesenchymal-tumour resected froma patient suffering from oncogenic hypophosphatemic osteomalacia; seeExample 4.

The phosphatonin nucleotide sequence identified as SEQ ID NO: 1 wasassembled from partially homologous (“overlapping”) sequences obtainedfrom related DMA clones. The overlapping sequences were assembled into asingle contiguous sequence of high redundancy (usually three to fiveoverlapping sequences at each nucleotide position), resulting in a finalsequence identified as SEQ ID NO: 1. Therefore, SEQ ID NO: 1 and thetranslated SEQ ID NO:2 are sufficiently accurate and otherwise suitablefor a variety of uses well known in the art and described further below.For instance, SEQ ID NO: 1 is useful for designing nucleic acidhybridization probes that will detect nucleic acid sequences containedin SEQ ID NO: 1. These probes will also hybridize to nucleic acidmolecules in biological samples, thereby enabling a variety of forensicand diagnostic methods of the invention. Similarly, polypeptidesidentified from SEQ ID NO:2 may be used to generate antibodies whichbind specifically to phosphatonin. Nevertheless, DNA sequences generatedby sequencing reactions can contain sequencing errors. The errors existas misidentified nucleotides, or as insertions or deletions ofnucleotides in the generated DNA sequence. The erroneously inserted ordeleted nucleotides cause frame shifts in the reading frames of thepredicted amino acid sequence. In these cases, the predicted amino acidsequence diverges from the actual amino acid sequence, even though thegenerated DNA sequence may be greater than 99.9% identical to the actualDNA sequence (for example, one base insertion or deletion in an openreading frame of over 1000 bases).

Accordingly, for those applications requiring precision in thenucleotide sequence or the amino acid sequence, the present inventionprovides not only the generated nucleotide sequence identified as SEQ IDNO: 1 and the predicted translated amino acid sequence identified as SEQID NO:2, but also means for the cloning of the cDNA and genomic DNAcorresponding to the nucleotide sequence in SEQ ID NO: 1. The nucleotidesequence of the so obtained phosphatonin clones can readily bedetermined by sequencing the clone in accordance with known methods. Thepredicted phosphatonin amino acid sequence can then be verified fromsuch cDNA or genomic clones. Moreover, the amino acid sequence of theprotein encoded by the obtained clones can also be directly determinedby peptide sequencing or by expressing the protein in a suitable hostcell, collecting the protein, and determining its sequence and functionaccording to the methods described herein.

The present invention also relates to the phosphatonin genecorresponding to SEQ ID NO: 1. The phosphatonin gene can be isolated inaccordance with known methods using the sequence information disclosedherein. Such methods include preparing probes or primers from thedisclosed sequence and identifying or amplifying the phosphatonin genefrom appropriate sources of genomic material. Also provided in thepresent invention are species homologs of phosphatonin. Species homologsmay be isolated and identified by making suitable probes or primers fromthe sequences provided herein and screening a suitable nucleic acidsource for the desired homologue.

Thus, by the provision of the nucleotide sequence of SEQ ID NO: 1 aswell as those encoding the amino acid sequence depicted in SEQ ID NO: 2,it is possible to isolate identical or similar nucleic acid moleculeswhich encode phosphatonin proteins from other species or organisms, inparticular orthologous phosphatonin genes from mammals other than human.The term “orthologous” as used herein means homologous sequences indifferent species that arose from a common ancestor gene duringspeciation. Orthologous genes may or may not be responsible for asimilar function; see, e.g., the glossary of the “Trends Guide toBioinformatics”, Trends Supplement 1998, Elsevier Science.

The phosphatonin polypeptides can be prepared in any suitable manner.Such polypeptides include isolated naturally occurring polypeptides,recombinantly produced polypeptides, synthetically producedpolypeptides, or polypeptides produced by a combination of thesemethods. Means for preparing such polypeptides are well understood inthe art.

Phosphatonin polypeptides are preferably provided in an isolated form,and preferably are substantially purified. A recombinantly producedversion of a phosphatonin polypeptide, including the secretedpolypeptide, can be substantially purified by the one-step methoddescribed in Smith and Johnson, Gene 67 (1988), 31-40. Phosphatoninpolypeptides also can be purified from natural or recombinant sourcesusing antibodies of the invention raised against the phosphatoninprotein in methods which are well known in the art.

Polynucleotide and Polypeptide Variants

“Variant” refers to a polynucleotide or polypeptide differing from thephosphatonin polynucleotide or polypeptide, but retaining essentialproperties thereof such as the immunological and preferably biologicalactivity referred to above. Generally, variants are overall closelysimilar, and, in many regions, identical to the phosphatoninpolynucleotide or polypeptide.

Such polynucleotides comprise those which encode fragments, analogues orderivatives and in particular orthologues of the above-describedphosphatonin proteins and differ, for example, by way of amino acidand/or nucleotide deletion(s), insertion(s), substitution(s),addition(s) and/or recombination(s) or any other modification(s) knownin the art either alone or in combination from the above-described aminoacid sequences or their underlying nucleotide sequence(s). Methods forintroducing such modifications in the nucleic acid molecules accordingto the invention are well-known to the person skilled in the art. Allsuch fragments, analogues and derivatives of the protein of theinvention are included within the scope of the present invention, aslong as the essential characteristic immunological and/or biologicalproperties as defined above remain unaffected in kind.

The term “variant” means in this context that the nucleotide and theirencoded amino acid sequence, respectively, of these polynucleotidesdiffers from the sequences of the above-described phosphatoninpolynucleotides and polypeptides in one or more nucleotide positions andare highly homologous to said nucleic acid molecules. Homology isunderstood to refer to a sequence identity of at least 40 %, preferably50 %, more preferably 60%, still more preferably 70 %, particularly anidentity of at least 80%, preferably more than 90% and still morepreferably more than 95%. The deviations from the sequences of thenucleic acid molecules described above can, for example, be the resultof nucleotide substitution(s), deletion(s), addition(s), insertion(s)and/or recombination(s); see supra. Homology can further imply that therespective nucleic acid molecules or encoded proteins are functionallyand/or structurally equivalent. The nucleic acid molecules that arehomologous to the nucleic acid molecules described above and that arederivatives of said nucleic acid molecules are, for example, variationsof said nucleic acid molecules which represent modifications having thesame biological function, in particular encoding proteins with the sameor substantially the same biological function. They may be naturallyoccurring variations, such as sequences from other mammals, ormutations. These mutations may occur naturally or may be obtained bymutagenesis techniques. The allelic variations may be naturallyoccurring allelic variants as well as synthetically produced orgenetically engineered variants; see supra.

By a polynucleotide having a nucleotide sequence at least, for example,95% “identical” to a reference nucleotide sequence of the presentinvention, it is intended that the nucleotide sequence of thepolynucleotide is identical to the reference sequence except that thepolynucleotide sequence may include up to five point mutations per each100 nucleotides of the reference nucleotide sequence encoding thephosphatonin polypeptide. In other words, to obtain a polynucleotidehaving a nucleotide sequence at least 95% identical to a referencenucleotide sequence, up to 5% of the nucleotides in the referencesequence may be deleted or substituted with another nucleotide, or anumber of nucleotides up to 5% of the total nucleotides in the referencesequence may be inserted into the reference sequence. The query sequencemay be an entire sequence shown of SEQ ID NO: 1, the ORF (open readingframe), or any fragment specified as described herein.

As a practical matter, whether any particular nucleic acid molecule orpolypeptide is at least 40%, 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%or 99% identical to a nucleotide sequence of the presence invention canbe determined conventionally using known computer programs. A preferredmethod for determining the best overall match between a query sequence(a sequence of the present invention) and a subject sequence, alsoreferred to as a global sequence alignment, can be determined using theFASTDB computer program based on the algorithm of Brutlag et al. (Comp.App. Biosci. 6 (1990), 237-245.) In a sequence alignment the query andsubject sequences are both DMA sequences. An RNA sequence can becompared by converting U's to T's. The result of said global sequencealignment is in percent identity. Preferred parameters used in a FASTDBalignment of DMA sequences to calculate percent identify are:Matrix=Unitary, k-tuple=4, Mismatch Penalty=1, Joining Penalty=30,Randomization Group Length=0, Cutoff Score=1, Gap Penalty=5, Gap SizePenalty 0.05, Window Size=500 or the length of the subject nucleotidesequence, whichever is shorter.

If the subject sequence is shorter than the query sequence because of 5′or 3′ deletions, not because of internal deletions, a manual correctionmust be made to the results. This is because the FASTDB program does notaccount for 5′ and 3′ truncations of the subject sequence whencalculating percent identity. For subject sequences truncated at the 5′or 3′ ends, relative to the query sequence, the percent identity iscorrected by calculating the number of bases of the query sequence thatare 5′ and 3′ of the subject sequence, which are not matched/aligned, asa percent of the total bases of the query sequence. Whether a nucleotideis matched/aligned is determined by results of the FASTDB sequencealignment. This percentage is then subtracted from the percent identity,calculated by the above FASTDB program using the specified parameters,to arrive at a final percent identity score. This corrected score iswhat is used for the purposes of the present invention. Only basesoutside the 5′ and 3′ bases of the subject sequence, as displayed by theFASTDB alignment, which are not matched/aligned with the query sequence,are calculated for the purposes of manually adjusting the percentidentity score.

For example, a 90 base subject sequence is aligned to a 100 base querysequence to determine percent identity. The deletions occur at the 5′end of the subject sequence and therefore, the FASTDB alignment does notshow a matched/alignment of the first 10 bases at 5′ end. The 10unpaired bases represent 10% of the sequence (number of bases at the 5′and 3′ ends not matched/total number of bases in the query sequence) so10% is subtracted from the percent identity score calculated by theFASTDB program. If the remaining 90 bases were perfectly matched thefinal percent identity would be 90%. In another example, a 90 basesubject sequence is compared with a 100 base query sequence. This timethe deletions are internal deletions so that there are no bases on the5′ or 3′ of the subject sequence which are not matched/aligned with thequery. In this case the percent identity calculated by FASTDB is notmanually corrected. Once again, only bases 5′ and 3′ of the subjectsequence which are not matched/aligned with the query sequence aremanually corrected for. No other manual corrections are to made for thepurposes of the present invention.

By a polypeptide having an amino acid sequence at least, for example,95% “identical” to a query amino acid sequence of the present invention,it is intended that the amino acid sequence of the subject polypeptideis identical to the query sequence except that the subject polypeptidesequence may include up to five amino acid alterations per each 100amino acids of the query amino acid sequence. In other words, to obtaina polypeptide having an amino acid sequence at least 95% identical to aquery amino acid sequence, up to 5% of the amino, acid residues in thesubject sequence may be inserted, deleted, added or substituted withanother amino acid. These alterations of the reference sequence mayoccur at the amino or carboxy terminal positions of the reference aminoacid sequence or anywhere between those terminal positions, interspersedeither individually among residues in the reference sequence or in oneor more contiguous groups within the reference sequence.

As a practical matter, whether any particular polypeptide is at least40%, 50%, 60%, 70%, 80%; 90%, 95%, 96%, 97%, 98% or 99% identical to,for instance, the amino acid sequences shown in SEQ ID NO: 2 can bedetermined conventionally using known computer programs. A preferredmethod for determining the best overall match between a query sequence(a sequence of the present invention) and a subject sequence, alsoreferred to as a global sequence alignment, can be determined using theFASTDB computer program based on the algorithm of Brutlag et al. (Comp.App. Biosci. 6 (1990), 237-245). In a sequence alignment the query andsubject sequences are either both nucleotide sequences or both aminoacid sequences. The result of said global sequence alignment is inpercent identity. Preferred parameters used in a FASTDB amino acidalignment are: Matrix=PAMO, k-tuple=2, Mismatch Penalty=1, JoiningPenalty=20, Randomization Group Length=0, Cutoff Score=1, Window Size=sequence length, Gap Penalty=5, Gap Size Penalty=0.05, Window Size=500or the length of the subject amino acid sequence, whichever is shorter.

If the subject sequence is shorter than the query sequence due to N- orC-terminal deletions, not because of internal deletions, a manualcorrection must be made to the results. This is because the FASTDBprogram does not account for N- and C-terminal truncations of thesubject sequence when calculating global percent identity. For subjectsequences truncated at the N- and C-termini, relative to the querysequence, the percent identity is corrected by calculating the number ofresidues of the query sequence that are N- and C-terminal of the subjectsequence, which are not matched/aligned with a corresponding subjectresidue, as a percent of the total bases of the query sequence. Whethera residue is matched/aligned is determined by results of the FASTDBsequence alignment. This percentage is then subtracted from the percentidentity, calculated by the above FASTDB program using the specifiedparameters, to arrive at a final percent identity score. This finalpercent identity score is what is used for the purposes of the presentinvention. Only residues to the N- and C-termini of the subjectsequence, which are not matched/aligned with the query sequence, areconsidered for the purposes of manually adjusting the percent identityscore. That is, only query residue positions outside the farthest N- andC-terminal residues of the subject sequence.

For example, a 90 amino acid residue subject sequence is aligned with a100 residue query sequence to determine percent identity. The deletionoccurs at the N-terminus of the subject sequence and therefore, theFASTDB alignment does not show a matching/alignment of the first 10residues at the N-terminus. The 10 unpaired residues represent 10% ofthe sequence (number of residues at the island C-termini notmatched/total number of residues in the query sequence) so 10% issubtracted from the percent identity score calculated by the FASTDBprogram. If the remaining 90 residues were perfectly matched the finalpercent identity would be 90%. In another example, a 90 residue subjectsequence is compared with a 100 residue query sequence. This time thedeletions are internal deletions so there are no residues at the N- orC-termini of the subject sequence which are not matched/aligned with thequery. In this case the percent identity calculated by FASTDB is notmanually corrected. Once again, only residue positions outside the N-and C-terminal ends of the subject sequence, as displayed in the FASTDBalignment, which are not matched/aligned with the query sequence aremanually corrected for. No other manual corrections are to made for thepurposes of the present invention.

The phosphatonin variants may contain alterations in the coding regions,non-coding regions, or both. Especially preferred are polynucleotidevariants containing alterations which produce silent substitutions,additions, or deletions, but do not alter the properties or activitiesof the encoded polypeptide. Nucleotide variants produced by silentsubstitutions due to the degeneracy of the genetic code are preferred.Moreover, variants in which 5-10, 1-5, or 1-2 amino acids aresubstituted, deleted, or added in any combination are also preferred.Phosphatonin polynucleotide variants can be produced for a variety ofreasons, e.g., to optimize codon expression for a particular host(change codons in the human mRNA to those preferred by a bacterial hostsuch as E. coli).

Naturally occurring phosphatonin variants are called “allelic variants,”and refer to one of several alternate forms of a gene occupying a givenlocus on a chromosome of an organism. (Genes II, Lewin, B., ed., JohnWiley & Sons, New York (1985) and updated versions). These allelicvariants can vary at either the polynucleotide and/or polypeptide level.Alternatively, non-naturally occurring variants may be produced bymutagenesis techniques or by direct synthesis. Using known methods ofprotein engineering and recombinant DNA technology, variants may begenerated to improve or alter the characteristics of the phosphatoninpolypeptides. For instance, one or more amino acids can be deleted fromthe N-terminus or C-terminus of the protein without substantial loss ofbiological function. The authors of Ron, J. Biol. Chem. 268 (1993),2984-2988, reported variant KGF proteins having heparin binding activityeven after deleting 3, 8, or 27 amino-terminal amino acid residues.Similarly, Interferon gamma exhibited up to ten times higher activityafter deleting 8-10 amino acid residues from the carboxy terminus ofthis protein. (Dobeli, J. Biotechnology 7 (1988), 199-216).

Moreover, ample evidence demonstrates that variants often retain abiological activity similar to that of the naturally occurring protein.For example, Gayle and coworkers (J. Biol. Chem. 268 (1993);22105-22111) conducted extensive mutational analysis of human cytokineIL-1a. They used random mutagenesis to generate over 3,500 individualIL-1a mutants that averaged 2.5 amino acid changes per variant over theentire length of the molecule. Multiple mutations were examined at everypossible amino acid position. The investigators found that “[m]ost ofthe molecule could be altered with little effect on either [binding orbiological activity]”; see Abstract. In fact, only 23 unique amino acidsequences, out of more than 3,500 nucleotide sequences examined,produced a protein that significantly differed in activity fromwild-type.

Furthermore, even if deleting one or more amino acids from theN-terminus or C-terminus of a polypeptide results in modification orloss of one or more biological functions, other biological activitiesmay still be retained. For example, the ability of a deletion variant toinduce and/or to bind antibodies which recognize the protein will likelybe retained when less than the majority of the residues of the proteinare removed from the N-terminus or C-terminus. Whether a particularpolypeptide lacking N- or C-terminal residues of a protein retains suchimmunogenic activities can readily be determined by routine methodsdescribed herein and otherwise known in the art. Furthermore, using thePESTFIND program (Rogers, Science 234 (1986), 364-368), PEST sequences(rich in proline, glutamic acid, serine, and threonine) can beidentified, which are characteristically present in unstable proteins.Such sequences may be removed from the phosphatonin proteins in order toincrease the stability and optionally the activity of the proteins.Methods for introducing such modifications in the nucleic acid moleculesaccording to the invention are well-known to the person skilled in theart.

Thus, the invention further includes phosphatonin polypeptide variantswhich show substantial biological activity. Such variants includedeletions, insertions, inversions, repeats, and substitutions selectedaccording to general rules known in the art so as have little effect onactivity. For example, guidance concerning how to make phenotypicallysilent amino acid substitutions is provided in Bowie, Science 247(1990), 1306-1310, wherein the authors indicate that there are two mainstrategies for studying the tolerance of an amino acid sequence tochange. The first strategy exploits the tolerance of amino acidsubstitutions by natural selection during the process of evolution. Bycomparing amino acid sequences in different species, conserved aminoacids can be identified. These conserved amino acids are likelyimportant for protein function. In contrast, the amino acid positionswhere substitutions have been tolerated by natural selection indicatesthat these positions are not critical for protein function. Thus,positions tolerating amino acid substitution could be modified whilestill maintaining biological activity of the protein.

The second strategy uses genetic engineering to introduce amino acidchanges at specific positions of a cloned gene to identify regionscritical for protein function. For example, site directed mutagenesis oralanine-scanning mutagenesis (introduction of single alanine mutationsat every residue in the molecule) can be used. (Cunningham and Wells,Science 244 (1989), 1081-1085) The resulting mutant molecules can thenbe tested for biological activity.

As the authors state, these two strategies have revealed that proteinsare surprisingly tolerant of amino acid substitutions. The authorsfurther indicate which amino acid changes are likely to be permissive atcertain amino acid positions in the protein. For example, most buried(within the tertiary structure of the protein) amino acid residuesrequire nonpolar side chains, whereas few features of surface sidechains are generally conserved. Moreover, tolerated conservative aminoacid substitutions involve replacement of the aliphatic or hydrophobicamino acids Ala, Val, Leu and lie; replacement of the hydroxyl residuesSer and Thr; replacement of the acidic residues Asp and Glu; replacementof the amide residues Asn and Gin, replacement of the basic residuesLys, Arg, and His; replacement of the aromatic residues Phe, Tyr, andTrp, and replacement of the small-sized amino acids Ala, Ser, Thr, Met,and Gly.

Besides conservative amino acid substitution, variants of phosphatonininclude (i) substitutions with one or more of the non-conserved aminoacid residues, where the substituted amino acid residues may or may notbe one encoded by the genetic code, or (ii) substitution with one ormore of amino acid residues having a substituent group, or (iii) fusionof the mature polypeptide with another compound, such as a compound toincrease the stability and/or solubility of the polypeptide (forexample, polyethylene glycol), or (iv) fusion of the polypeptide withadditional amino acids, such as an IgG Fc fusion region peptide, orleader or secretary sequence, or a sequence facilitating purification.Such variant polypeptides are deemed to be within the scope of thoseskilled in the art from the teachings herein. For example, phosphatoninpolypeptide variants containing amino acid substitutions of chargedamino acids with other charged or neutral amino acids may produceproteins with improved characteristics, such as less aggregation.Aggregation of pharmaceutical formulations both reduces activity andincreases clearance due to the aggregate's immunogenic activity; see,e.g. Pinckard, Clin. Exp. Immunol. 2 (1967), 331-340; Bobbins, Diabetes36 (1987), 838-845; Cleland, Crit. Rev. Therapeutic Drug Carrier Systems10 (1993), 307-377.

Polynucleotide and Polypeptide Fragments

In the present invention, a “polynucleotide fragment” refers to a shortpolynucleotide having a nucleic acid sequence contained in SEQ ID NO: 1.The short nucleotide fragments are preferably at least about 15 nt, andmore preferably at least about 20 nt, still more preferably at leastabout 30 nt, and even more preferably, at least about 40 nt in length. Afragment “at least 20 nt in length,” for example, is intended to include20 or more contiguous bases from the cDNA sequence contained in thenucleotide sequence shown in SEQ ID NO: 1. These nucleotide fragmentsare useful as diagnostic probes and primers as discussed herein. Ofcourse, larger fragments (e.g., 50, 150, 500, 600, 1000 nucleotides) arepreferred.

Moreover, representative examples of phosphatonin polynucleotidefragments include, for example, fragments having a sequence from aboutnucleotide number 1-50, 51-100, 101-150, 151-200, 201-250, 251-300,301-350, 351-400, 401-450, 451-500, 501-550, 551-600, 651-700, 701-750,751-800, 800-850, 851-900, 901-950, 951-1000, 1001-1050, 1051-1100,1101-1150, 1151-1200, 1201-1250, 1251-1300 or 1301-1350 of SEQ ID NO:1.In this context “about” includes the particularly recited ranges, largeror smaller by several (5, 4, 3, 2, or 1) nucleotides, at either terminusor at both termini. Preferably, these fragments encode a polypeptidewhich has biological activity. More preferably, these polynucleotidescan be used as probes or primers as discussed herein.

In the present invention, a “polypeptide fragment” refers to a shortamino acid sequence contained in SEQ ID NO:2. Protein fragments may be“free-standing,” or comprised within a larger polypeptide of which thefragment forms a part or region, most preferably as a single continuousregion. Representative examples of polypeptide fragments of theinvention, include, for example, fragments from about amino acid number1-20, 21-40, 41-60, 61-80, 81-100, 102-120, 121-140, 141-160, 161-180,181-200, 201-220, 221-240, 241-260, 261-280, 281-300, 301-320, or321-340, 341-360, 361-380, 381-400 and 401-421 to the end of the codingregion. Moreover, polypeptide fragments can be about 20, 30, 40, 50, 60,70, 80, 90, 100, 110, 120, 130, 140, or 150 amino acids in length. Inthis context “about” includes the particularly recited ranges, larger orsmaller by several (5, 4, 3, 2, or 1) amino acids, at either extreme orat both extremes.

Preferred polypeptide fragments include the phosphatonin protein havinga continuous series of deleted residues from the amino or the carboxyterminus, or both. For example, any number of amino acids, ranging from1-60, can be deleted from the amino terminus of the phosphatoninpolypeptide. Similarly, any number of amino acids, ranging from 1-30,can be deleted from the carboxy terminus of the phosphatonin protein.Furthermore, any combination of the above amino and carboxy terminusdeletions are preferred. Similarly, polynucleotide fragments encodingthese phosphatonin polypeptide fragments are also preferred.Particularly, N-terminal deletions of the phosphatonin polypeptide canbe described by the general formula m-430, where m is an integer from 2to 416 where m corresponds to the position of the amino acid residueidentified in SEQ ID NO:2.

Also preferred are phosphatonin polypeptide and polynucleotide fragmentscharacterized by structural or functional domains. Preferred embodimentsof the invention include fragments that comprise alpha-helix andalpha-helix forming regions (“alpha-regions”), beta-sheet andbeta-sheet-forming regions (“beta-regions”), turn and turn-formingregions (“turn-regions”), coil and coil-forming regions(“coil-regions”), hydrophilic regions, hydrophobic regions, alphaamphipathic regions, beta amphipathic regions, flexible regions,surface-forming regions, substrate binding region, and high antigenicindex regions. As set out in the Figures, such preferred regions includeGarnier-Robson alpha-regions, beta-regions, turn-regions, andcoil-regions, Chou-Fasman alpha-regions, beta-regions, and turn-regions,Kyte-Doolittle hydrophilic regions and hydrophobic regions, Eisenbergalpha and beta amphipathic regions, Karplus-Schulz flexible regions,Emini surface-forming regions, and Jameson-Wolf high antigenic indexregions. Polypeptide fragments of SEQ ID NO:2 falling within conserveddomains are specifically contemplated by the present invention and shownin the Figures. Moreover, polynucleotide fragments encoding thesedomains are also contemplated.

Other preferred fragments are biologically active phosphatoninfragments. Biologically active fragments are those exhibiting activitysimilar, but not necessarily identical, to an activity of thephosphatonin polypeptide. The biological activity of the fragments mayinclude an improved desired activity, or a decreased undesirableactivity.

However, many polynucleotide sequences, such as EST sequences, arepublicly available and are accessible through sequence databases. Someof these sequences may be related to SEQ ID NO: 1 and may have beenpublicly available prior to conception of the present invention.Preferably, such related polynucleotides are specifically excluded fromthe scope of the present invention. To list every related sequence wouldbe cumbersome.

Accordingly, preferably excluded from the present invention are one ormore polynucleotides comprising a nucleotide sequence described by thegeneral formula of a-b, where a is any integer between 1 to 1655 of SEQID NO:1, b is an integer of 15 to 1655, where both a and b correspond tothe positions of nucleotide residues shown in SEQ ID NO: 1, and wherethe b is greater than or equal to a+14.

Epitopes & Antibodies

In the present invention, “epitopes” refer to phosphatonin polypeptidefragments having antigenic or immunogenic activity in an animal, e.g., arat, a rabbit, a human, a mouse (including a transgenic mouse whichcarry human immunoglobulin genes and produce human antibody molecules),and so on. A preferred embodiment of the present invention relates to aphosphatonin polypeptide fragment comprising an epitope, as well as thepolynucleotide encoding this fragment. A region of a protein molecule towhich an antibody can bind is defined as an “antigenic epitope.” Incontrast, an “immunogenic epitope” is defined as a part of a proteinthat elicits an antibody response; see, for instance, Geysen, Proc.Natl. Acad. Sci. USA 81 (1983); 3998-4002. Fragments which function asepitopes may be produced by any conventional means; see, e.g., Houghten,Proc. Natl. Acad. Sci. USA 82 (1985), 5131-5135 further described inU.S. Pat. No. 4,631,211.

In the present invention, antigenic epitopes preferably contain asequence of at least seven, more preferably at least nine, and mostpreferably between about 15 to about 30 amino acids. Antigenic epitopesare useful to raise antibodies, including monoclonal antibodies, thatspecifically bind the epitope; see, for instance, Wilson, Cell 37(1984), 767-778; Sutcliffe, Science 219 (1983), 660-666.)

Similarly, immunogenic epitopes can be used to induce antibodiesaccording to methods well known in the art; see, for instance,Sutcliffe, supra; Wilson, supra; Chow, Proc. Natl. Acad. Sci. USA 82(1985), 910-914; and Bittle, J. Gen. Virol. 66 (1985); 2347-2354. Apreferred immunogenic epitope includes the soluble protein. Theimmunogenic epitopes may be presented together with a carrier protein,such as an albumin, to an animal system (such as rabbit or mouse) or, ifit is long enough (at least about 25 amino acids), without a carrier.However, immunogenic epitopes comprising as few as 8 to 10 amino acidshave been shown to be sufficient to raise antibodies capable of bindingto, at the very least, linear epitopes in a denatured polypeptide (e.g.,in Western blotting.)

Using the computer program GCG-Peptide-structure (Rice, Programme Manualfor the EGCG package, Cambridge, CB10 1RQ England: Hinxton Hall; 1995)available from the Human Genome Resource Centre(http://www.hqmp.mrc.ac.uk/homepaqe.htmn. SEQ ID NO:2 was foundantigenic at amino acids: regions shown in FIG. 4. Thus, these regionscould be used as epitopes to produce antibodies against the proteinencoded by SEQ ID No: 1.

As used herein, the term “antibody” (Ab) or “monoclonal antibody” (Mab)is meant to include intact molecules as well as antibody fragments (suchas, for example, Fab and F(ab′)₂ fragments) which are capable ofspecifically binding to protein. Fab and F(ab′)₂ fragments lack the Fcfragment of intact antibody, clear more rapidly from the circulation,and may have less non-specific tissue binding than an intact antibody;see, e.g., Wahl, J. Nucl. Med. 24 (1983), 316-325. Thus, these fragmentsare preferred, as well as the products of a FAB or other immunoglobulinexpression library. Moreover, antibodies of the present inventioninclude chimeric, single chain, humanized antibodies, human antibodiesobtainable by or from phage display, a transgenic mouse carrying humanimmunoglobulin genes and/or human chromosomes, isolated immune cellsfrom human body, in vitro or ex vivo immunization of human immune cells,or any other available methods.

In another embodiment, the present invention relates to a nucleic acidmolecule which hybridizes with the complementary strand of thephosphatonin polynucleotide of the invention and which encodes a mutatedversion of the protein as defined above which has lost itsimmunological, preferably biological activity. This embodiment may proveuseful for, e.g., generating dominant mutant alleles of theabove-described phosphatonin proteins. Said mutated version ispreferably generated by substitution, deletion and/or addition of 1 to 5or 5 to 10 amino acid residues in the amino acid sequence of theabove-described wild type proteins.

Vectors, Host Cells and Protein Production

The present invention also relates to vectors containing thephosphatonin polynucleotide, host cells, and the production ofpolypeptides by recombinant techniques. The vector may be, for example,a phage, plasmid, viral, or retroviral vector. Retroviral vectors may bereplication competent or replication defective. In the latter case,viral propagation generally will occur only in complementing host cells.

Phosphatonin polynucleotides may be joined to a vector containing aselectable marker for propagation in a host. Generally, a plasmid vectoris introduced in a precipitate, such as a calcium phosphate precipitate,or in a complex with a charged lipid. If the vector is a virus, it maybe packaged in vitro using an appropriate packaging cell line and thentransduced into host cells.

The phosphatonin polynucleotide insert should be operatively linked toan appropriate promoter, such as the phage lambda PL promoter, the E.coli lac, trp, phoA and tac promoters, the SV40 early and late promotersand promoters of retroviral LTRs, to name a few. Other suitablepromoters will be known to the skilled artisan. The expressionconstructs will further contain sites for transcription initiation,termination, and, in the transcribed region, a ribosome binding site fortranslation. The coding portion of the transcripts expressed by theconstructs will preferably include a translation initiating codon at thebeginning and a termination codon (UAA, UGA or UAG) appropriatelypositioned at the end of the polypeptide to be translated.

As indicated, the expression vectors will preferably include at leastone selectable marker. Such markers include dihydrofolate reductase,G418 or neomycin resistance for eukaryotic cell culture andtetracycline, kanamycin or ampicillin resistance genes for culturing inE. coli and other bacteria. Representative examples of appropriate hostsinclude, but are not limited to, bacterial cells, such as E. coli,Streptomyces and Salmonella typhimurium cells; fungal cells, such asyeast cells; insect cells such as Drosophila S2 and Spodoptera Sf9cells; animal cells such as CHO, COS, 293, and Bowes melanoma cells; andplant cells. Appropriate culture mediums and conditions for theabove-described host cells are known in the art. Among vectors preferredfor use in bacteria include pQE70, pQEGO and pQE-9, available fromQIAGEN, Inc.; pBluescript vectors, Phagescript vectors, pNHSA, pNH16a,pNH18A, pNH46A, available from Stratagene Cloning Systems, Inc.; andptrc99a, pKK223-3, pKK233-3, pDR540, pRITS available from PharmaciaBiotech, Inc. Among preferred eukaryotic vectors are pWLNEO, pSV2CAT,pOG44, pXTI and pSG available from Stratagene; and pSVKS, pBPV, pMSG andpSVL available from Pharmacia. Other suitable vectors will be readilyapparent to the skilled artisan.

Furthermore, one could use, e.g., a mammalian cell that alreadycomprises in its genome a nucleic acid molecule encoding a phosphatoninpolypeptide as described above, but does not express the same or not inan appropriate manner due to, e.g., a weak promoter, and introduce intothe mammalian cell an expression control sequence such as a strongpromoter in close proximity to the endogenous nucleic acid moleculeencoding said phosphatonin poiypeptide so as to induce expression of thesame.

In this context the term “expression control sequence” denotes a nucleicacid molecule that can be used to increase the expression of thephosphatonin polypeptide, due to its integration into the genome of acell in close proximity to the phosphatonin encoding gene. Suchregulatory sequences comprise promoters, enhancers, inactivated silencerintron sequences, 3′UTR and/or 5′UTR coding regions, protein and/or RNAstabilizing elements, nucleic acid molecules encoding a regulatoryprotein, e.g., a transcription factor, capable of inducing or triggeringthe expression of the phosphatonin gene or other gene expression controlelements which are known to activate gene expression and/or increase theamount of the gene product. The introduction of said expression controlsequence leads to increase and/or induction of expression ofphosphatonin polypeptides, resulting in the end in an increased amountof phosphatonin polypeptides in the cell. Thus, the present invention isaiming at providing de novo and/or increased expression of phosphatoninpolypeptides.

Introduction of the construct into the host cell can be effected bycalcium phosphate transfection, DEAE-dextran mediated transfection,cationic lipid-mediated transfection, electroporation, transduction,infection, or other methods. Such methods are described in many standardlaboratory manuals, such as Davis, Basic Methods In Molecular Biology(1986). It is specifically contemplated that phosphatonin polypeptidesmay in fact be expressed by a host cell lacking a recombinant vector.

Phosphatonin polypeptides can be recovered and purified from recombinantcell cultures by well-known methods including ammonium sulfate orethanol precipitation, acid extraction, anion or cation exchangechromatography, phosphocellulose chromatography, hydrophobic interactionchromatography, affinity chromatography, hydroxylapatite chromatographyand lectin chromatography. Most preferably, high performance liquidchromatography (“HPLC”) is employed for purification.

Phosphatonin polypeptides can also be recovered from: products purifiedfrom natural sources, including bodily fluids, tissues and cells,whether directly isolated or cultured; products of chemical syntheticprocedures; and products produced by recombinant techniques from aprokaryotic or eukaryotic host, including, for example, bacterial,yeast, higher plant, insect, and mammalian cells. Depending upon thehost employed in a recombinant production procedure, the phosphatoninpolypeptides may be glycosylated or may be non-glycosylated. Inaddition, phosphatonin polypeptides may also include an initial(modified) methionine residue, in some cases as a result ofhost-mediated processes. Thus, it is well known in the art that theN-terminal methionine encoded by the translation initiation codongenerally is removed with high efficiency from any protein aftertranslation in all eukaryotic cells. While the N-terminal methionine onmost proteins also is efficiently removed in most prokaryotes, for someproteins, this prokaryotic removal process is inefficient, depending onthe nature of the amino acid to which the N-terminal methionine iscovalently linked.

In a particularly preferred embodiment, the present invention relates toa process for isolating a phosphatonin polypeptide comprising the stepsof:

-   -   (a) culturing tumor-conditioned media or osteosarcoma cells to        confluence in serum supplemented media (DMEM Eagles/10%        FCS/glutamine/antimycotic(DMFCS);    -   (b) incubating the cells on alternate days in serum free media        DMEM Eagles/glutamine/antimycotic antibiotic (DM) up to five        hours;    -   (c) collecting conditioned serum free media from the cells and        equilibrating the conditioned media to 0.06M sodium phosphate pH        7.2 and 0.5 M NaCI (PBS);    -   (d) subjecting the media from (c) to an equilibrated column of        concanavilin A sepharose;    -   (e) washing the column extensively with PBS;    -   (f) eluting the concanavalin A column with PBS supplemented with        0.5 M cc-methyl-D-glucopyranoside;    -   (g) subjecting the eluted material from (f) to cation exchange        chromatography; and    -   (h) eluting phosphatonin polypeptide containing fractions with        0.5 M NaCI.

The above-described method is illustrated in Example 1.

Another subject of the invention is a method for the preparation ofphosphatonin polypeptides which comprises the cultivation of host cellsaccording to the invention which, due to the presence of a vector or apolynucleotide according to the invention or an exogenous expressioncontrol sequence, are able to express such a polypeptide, underconditions which allow expression of the polypeptide and recovering ofthe so-produced polypeptide from the culture. It is also to beunderstood that the proteins can be expressed in a cell free systemusing for example in vitro translation assays known in the art.

Hence, in a still further embodiment, the present invention relates to aphospatonin polypeptide or an immunologically and/or biologically activefragment thereof encoded by the polynucleotide of the invention orproduced by a method of as described above. Likewise phosphatoninpolypeptides are within the scope of the present invention which areobtainable by proteolytic cleavage of the above described phosphatoninpolypeptides by a PHEX metallopeptidase.

It will be apparent to those skilled in the art that the protein of theinvention can be further coupled to other moieties as described abovefor, e.g., drug targeting and imaging applications. Such coupling may beconducted chemically after expression of the protein to site ofattachment or the coupling product may be engineered into the protein ofthe invention at the DMA level. The DMAs are then expressed in asuitable host system, and the expressed proteins are collected andrenatured, if necessary.

Regulation of a Phosphate Metabolism

As mentioned hereinbefore, the phosphatonin polypeptide of the presentinvention is capable of regulating phosphate metabolism in differentways. Thus, in one embodiment, the present invention relates to aphosphatonin polypeptide having phosphatonin activity in that it has atleast one of the following activities:

-   -   (a) it is capable of down-regulating sodium dependent phosphate        co-transport;    -   (b) it is capable of up-regulating renal 25-hydroxy vitamin        D3-24-hydroxylase; and/or    -   (c) it is capable of down-regulating renal        25-hydroxy-D-1-α-hydroxylase.

In another embodiment, the present invention relates to a phosphatoninpolypeptide having anti-phosphatonin activity in that it has at leastone of the following activities:

-   -   (a) it is capable of up-regulating sodium dependent phosphate        co-transport;    -   (b) it is capable of down-regulating renal 25-hydroxy vitamin        D3-24-hydroxylase; and/or    -   (c) it is capable of up-regulating renal        25-hydroxy-D-1-α-hydroxylase.

In a particularly preferred embodiment of the present invention, thephosphatonin polypeptide comprises a bone mineral motif as describedabove and positively regulates bone mineralization.

In a still further embodiment, the present invention relates tophosphatonin polypeptides which have lost at least one of the abovedescribed activities. Such polypeptides may be mutant forms of thephosphatonin polypeptide of the present invention and can, e.g., be usedfor studying the effect of mutations in the phosphatonin encoding gene.In particular, such mutants may prove useful for the development ofdrugs that are capable of compensating a deficiency caused by the lossof one of the biological activities of the wildtype phosphatonin. Suchmutant forms of phosphatonin polypeptides may best be studied in thescreening methods described in more detail hereinbelow.

Phosphatonin antibodies

Furthermore, as described above, the provision of the phosphatoninpolypeptide of the present invention enables the production ofphosphatonin specific antibodies. In this respect, hybridoma technologyenables production of cell lines secreting antibody to essentially anydesired substance that produces an immune response. RNA encoding thelight and heavy chains of the immunoglobulin can then be obtained fromthe cytoplasm of the hybridoma. The 5′ end portion of the mRNA can beused to prepare cDNA to be inserted into an expression vector. The DNAencoding the antibody or its immunoglobulin chains can subsequently beexpressed in cells, preferably mammalian cells. Depending on the hostcell, renaturation techniques may be required to attain properconformation of the antibody. If necessary, point substitutions seekingto optimize binding may be made in the DNA using conventional cassettemutagenesis or other protein engineering methodology such as isdisclosed herein.

Thus, the present invention also relates to an antibody specificallyrecognizing the phosphatonin polypeptide of the invention.

In a preferred embodiment of the invention, said antibody is amonoclonal antibody, a polyclonal antibody, a single chain antibody,human or humanized antibody, primatized, chimerized or fragment thereofthat specifically binds said peptide or polypeptide also includingbispecific antibody, synthetic antibody, antibody fragment, such as Fab,Fv or scFv fragments etc., or a chemically modified derivative of any ofthese. The general methodology for producing antibodies is well-knownand has been described in, for example, Köhler and Milstein, Nature 256(1975), 494 and reviewed in J.G.R. Hurrel, ed, “Monoclonal HybridomaAntibodies: Techniques and Applications”, CRC Press Inc., Boco Raron,Fla. (1982), as well as that taught by L T. Mimms et al., Virology 176(1990), 604-619. Furthermore, antibodies or fragments thereof to theaforementioned peptides can be obtained by using methods which aredescribed, e.g., in Harlow and Lane “Antibodies, A Laboratory Manual”,CSH Press, Cold Spring Harbor, 1988.

For the production of antibodies in experimental animals, various hostsincluding goats, rabbits, rats, mice, and others, may be immunized byinjection with polypeptides of the present invention or any fragment oroligopeptide or derivative thereof which has immunogenic properties.Techniques for producing and processing polyclonal antibodies are knownin the art and are described in, among others, Mayer and Walker, eds.,“Immunochemical Methods in Cell and Molecular Biology”, Academic Press,London (1987). Polyclonal antibodies also may be obtained from ananimal, preferably a mammal. Methods for purifying antibodies are knownin the art and comprise, for example, immunoaffinity chromatography.Depending on the host species, various adjuvants or immunologicalcarriers may be used to increase immunological responses. Such adjuvantsinclude, but are not limited to, Freund's, complete or incompleteadjuvants, mineral gels such as aluminium hydroxide, and surface activesubstances such as lysolecithin, pluronic polyols, polyanions, peptides,oil emulsions and dinitrophenol. An example of a carrier, to which, forinstance, a peptide of the invention may be coupled, is keyhole limpethemocyanin (KLH).

The production of chimeric antibodies is described, for example, inWO89/09622. Methods for the production of humanized antibodies aredescribed in, e.g., EP-A1 0 239 400 and WO90/07861. A further source ofantibodies to be utilized in accordance with the present invention areso-called xenogenic antibodies. The general principle for the productionof xenogenic antibodies such as human antibodies in mice is describedin, e.g., WO 91/10741, WO 94/02602, WO 96/34096 and WO 96/33735.

In a preferred embodiment, the antibody of the invention has an affinityof at least about 10⁻⁷ M, preferably at least about 10⁻⁸ M morepreferably at least about 10⁻⁹ M and most preferably at least about10⁻¹⁰ M. On the other hand, the phosphatonin antibody may have a bindingaffinity of about 10⁵ M⁻¹, preferably not higher than 10⁷ M⁻¹ ifstimulation of phosphatonin activity is envisaged and advantageously upto 10¹⁰ M⁻¹ or more in case phosphatonin activity should be suppressed.

Uses of the Phosphatonin Polynucleotides

The phosphatonin polynucleotides identified herein can be used innumerous ways as reagents. The following description should beconsidered exemplary and utilizes known techniques.

There exists an ongoing need to identify new chromosome markers, sincefew chromosome marking reagents, based on actual sequence data (repeatpolymorphisms), are presently available. Phosphatonin relatedpolynucleotides (genomic and/or cDNA) can be used to carry outrestriction analysis as described in detail (Rowe, Hum. Genet. 94:5(1994), 457-467; Benham, Genomics 12 (1992), 368-376; Gillett, Ann. Hum.Genet. 60(3) (1996), 201-211; Rowe, Nucleic Acids Res. 22(23) (1994),5135-5136). In particular, the use of microsatellites (Rowe, Hum. Genet.94:5 (1994), 457-467; Rowe, Nucleic Acids Res. 22(23) (1994), 5135-5136;Rowe, Hum. Genet. 93 (1994), 291-294; Rowe, Hum. Genet. 91 (1993),571-575; Rowe, Hum. Genet. 97 (1996), 345-352; Rowe, Hum. Genet. 89(1992), 539-542), and the isolation of informative markers usingirradiation-fusion-gene-transfer hybrids and ALU-PCR (Benham, Genomics12 (1992), 368-376) will enable the rapid isolation of highlyinformative methods for the screening of phosphatonin and derivativeinherited diseases. The above methodologies have been particularlysuccessful in the mapping and localization of the PHEX gene (MERE isproposed to a PHEX substrate), and extensive mutation analysis hasrevealed structural regions and motifs prerequisite for PHEXbio-activity (Rowe, Hum. Mol. Genet. 6 (1997), 539-549; Rowe, Exp.Nephrol. 5 (1997), 355-363; Rowe, Current Opinion in Nephrology &Hypertension 7(4) (1998), 367-376; Rowe, Clinical and ExperimentalNephrology 2(3) (1998), 183-193), these same approaches can be used forphosphatonin. More recently powerful genome-wide linkage and screeningtechniques have been developed that rely on single nucleotidepolymorphisms (SNP's), and the use of a combination of gel-basedsequencing and high-density variation-detection DNA chips (Wang, Science280 (1998), 1077-1082). Recently SNP data has been made available on theinternet by the Center for Genome Research at the Whitehead Institutefor Biomedical Research in Cambridge, Massachusetts, USA (Whitehead-MIT)at http://www-qenome.wi.mit.edu/SNP/human/index.html. This powerful newoligonucleotide-array based methodology will be the future route formolecular expression analysis, polymorphism and genotyping, and diseasemanagement (Wang, Science 280 (1998), 1077-1082; Chee, Science 274(1996), 610-614; Gentalen, Nucleic Acids Res. 27 (1999), 1485-1491;Hacia, Nucleic Acids Res. 26 (1998), 3865-3866; Lipshutz, Nat. Genet. 21(1999), 20-24; Fan, Eur. J. Hum. Genet. 6 (1998), 134). Given thesequence information for MEPE in this application the above newapproaches and technology will be used to address the areas described.The sequence may be mapped to a particular chromosome or to a specificregion of the chromosome using well known techniques. These include insitu hybridization to chromosomal spreads, flow-sorted chromosomalpreparations, or artificial chromosome constructions such as yeastartificial chromosomes, bacterial artificial chromosomes, bacterial P1constructions or single chromosome cDNA libraries as reviewed in Price(Blood Rev. 7 (1993), 127-134) and Trask (Trends Genet. 7 (1991),149-154). The technique of fluorescent in situ hybridization ofchromosome spreads has been described, among other places, in Verma,(1988) Human Chromosomes: A Manual of Basic Techniques, Pergamon Press,New York N.Y. Fluorescent in situ hybridization of chromosomalpreparations and other physical chromosome mapping techniques may becorrelated with additional genetic map data. Extensive mapping dataaccessible to the scientific community can be found on the internet atsites sponsored by the Human-Genome-Mapping-Project United Kingdom(HGMP-RC) http://www.hqmp.mrc.ac.uk/homepaqe.html. the NationalCollection of biological information (NCBI) sponsored by the NationalInstitute of Health USA (NIH), http://ww.ncbi.nlm.nih.gov/, also theCenter for Genome Research at the Whitehead Institute for BiomedicalResearch in Cambridge, Mass., USA (Whitehead-MIT)http://www-qenome.wi.mit.edu/. Moreover, extensive microsatellite-mapsand related mapping tools covering the entire human genome can also beaccessed via Genethon (French Government sponsored database)http://www.qenethon.fr/qenethon en.html. Seminal maps have also beenpublished in Science and Nature (see, for example, Dib, Nature 380(1996), 152-154), but for up to date data the internet sites should beconsulted. Correlation between the location of the gene encoding aphosphatonin polypeptide of the invention on a physical chromosomal mapand a specific feature, e.g., a hypo- or hyperphosphatemic disease mayhelp to delimit the region of DNA associated with this feature. Thenucleotide sequences of the subject invention may be used to detectdifferences in gene sequences between normal, carrier or affectedindividuals. Furthermore, the means and methods described herein can beused for marker-assisted animal breeding. The nucleotide sequence of thesubject invention may also be used to detect differences in thechromosomal location due to translocation, inversion, etc. among normal,carrier or affected individuals.

In the very least, the phosphatonin polynucleotides can be used asmolecular weight markers on Southern gels, as diagnostic probes for thepresence of a specific mRNA in a particular cell type, as a probe to“subtract-out” known sequences in the process of discovering novelpolynucleotides, for selecting and making oligomers for attachment to a“gene chip” or other support, to raise anti-DNA antibodies using DNAimmunization techniques, and as an antigen to elicit an immune response.

Uses of Phosphatonin Polypeptides and Antibodies

Phosphatonin polypeptides and antibodies thereto can be used in numerousways. The following description should be considered exemplary andutilizes known techniques.

Phosphatonin polypeptides can be used to assay protein levels in abiological sample using antibody-based techniques. For example, proteinexpression in tissues can be studied with classical immunohistologicalmethods; see, e.g., Jalkanen, J. Cell. Biol. 101 (1985), 976-985;Jalkanen, J. Cell. Biol. 105 (1987), 3087-3096.) Other antibody basedmethods useful for detecting protein gene expression includeimmunoassays, such as the enzyme linked immunosorbent assay (ELISA) andthe radioimmunoassay (RIA). Suitable antibody assay labels are known inthe art and include enzyme labels, such as, glucose oxidase, andradioisotopes, such as iodine (1251, 121I), carbon (14C), sulfur (35S),tritium (3H), indium (112In), and technetium (99mTc), and fluorescentlabels, such as fluorescein and rhodamine, and biotin.

In addition to assaying protein levels in a biological sample, proteinscan also be detected in vivo by imaging. Antibody labels or markers forin vivo imaging of protein include those detectable by X-radiography,NMR or ESR. For X-radiography, suitable labels include radioisotopessuch as barium or cesium, which emit detectable radiation but are notovertly harmful to the subject. Suitable markers for NMR and ESR includethose with a detectable characteristic spin, such as deuterium, whichmay be incorporated into the antibody by labeling of nutrients for therelevant hybridoma.

A protein-specific antibody or antibody fragment which has been labeledwith an appropriate detectable imaging moiety, such as a radioisotope(for example, ¹³¹I, ¹²¹In, ⁹⁹mTc), a radio-opaque substance, or amaterial detectable by nuclear magnetic resonance, is introduced (forexample, parenterally, subcutaneously, or intraperitoneally) into themammal. It will be understood in the art that the size of the subjectand the imaging system used will determine the quantity of imagingmoiety needed to produce diagnostic images. In the case of aradioisotope moiety, for a human subject, the quantity of radioactivityinjected will normally range from about 5 to 20 millicuries of 99mTc.The labeled antibody or antibody fragment will then preferentiallyaccumulate at the location of cells which contain the specific protein.In vivo tumor imaging is described in, e.g., Burchiel,“Immunopharmacokinetics of Radiolabeled Antibodies and Their Fragments”,Chapter 13 in Tumor Imaging: The Radiochemical Detection of Cancer,Burchiel and Rhodes, eds., Masson Publishing Inc. (1982).

Thus, the invention provides a diagnostic method of a disorder, whichinvolves (a) assaying the expression of phosphatonin polypeptide incells or tissues, or the level of phosphatonin or its active fragmentsor epitopes in the body fluid of an individual; (b) comparing the levelof gene expression with a standard gene expression level, whereby anincrease or decrease in the assayed phosphatonin polypeptide geneexpression level compared to the standard expression level is indicativeof a disorder.

Moreover, phosphatonin polypeptides can be used to treat disease. Forexample, patients can be administered phosphatonin polypeptides in aneffort to increase or decrease serum phosphate level and/or improve theimpaired bone formation (X-Linked Hyophosphatemic Rickets, OncogenicHypophosphatemic Osteomalacia, Renal Failure, Osteoporosis, RenalOsteodystrophy, and so forth). It can activate or inhibit its receptorsto up- or down-regulate the expression of sodium dependent phosphateco-transporters. In addition, the phosphatonin gene promoter and/orenhancer element can be used in gene therapy applications for treatingphosphate metabolism-specific disorders, particularly X-LinkedHypophosphatemic Rickets. Also, possibly in bone-mineral loss disorderswhere inappropriate gene regulation and/or post-translationalmodification of MEPE occurs due to undefined secondary or primarychanges (e.g., postmenopausal women, osteoposis, age related), wheresupplementation of the hormone (and/or agonists-antagonists to receptoror hormone) perhaps as an adjunct to hormone replacement therapy wouldrestore phosphate and bone-mineral balance. A key feature of MEPEbio-activity and, thus, disease-treatment is the prediction thatN-terminal sequence regulates renal phosphate uptake, and the C-terminus(notably regions associated with the MEPE-motif described earlier) ispre-requisite for normal bone mineralization and growth.

After renal-transplantation, chronic hyperphosphatemia or in some caseshypophosphatemia are key features that result in major clinicalcomplications. For example, renal transplantation of a normal kidneyinto a male HYP patient was reported to result in pathophysiologicalchanges in the normal transplanted kidney such that a “rickets-type”renal phosphate leak developed (Morgan, Arch. Intern. Med. 134 (1974),549-552). The clinical use of N-terminal-cleaved processed fragments ofMEPE could result in effective anti-hypophosphatemic therapy. Incontrast, renal-transplantation cases that result in hyperphosphatemiacould be treated with whole recombinant MEPE or active derivativepeptides modeled on distinct N-terminal residues. Other diseases thatcould benefit from treatment with MEPE, MEPE derivative peptides,receptor antagonists-agonists (peptides could be modified to increasepotency and specificity of action) include renal osteodystrophy, renaltoxicity, Pagets disease of bone, autosomal-forms of rickets, certainforms of renal Fanconi syndrome. Moreover, if receptors are expressed ina range of tissues (intestines, etc.) as well as the kidney, then thepotential for treating patients with end stage renal disease exists(i.e. complete loss of kidney function).

Similarly, antibodies directed to phosphatonin polypeptides can also beused to treat disease. For example, administration of an antibodydirected to a phosphatonin polypeptide can bind and reduceoverproduction of the polypeptide. Similarly, administration of anantibody can activate the polypeptide, such as by binding to apolypeptide and cleaving it to a different activity form.

At the very least, the phosphatonin polypeptides can be used asmolecular weight markers on SDS-PAGE gels or on molecular sieve gelfiltration columns using methods well known to those of skill in theart. Phosphatonin polypeptides can also be used to raise antibodies,which in turn are used to measure protein expression from a recombinantcell, as a way of assessing transformation of the host cell.

Furthermore, phosphatonin polynucleotides and polypeptides can be usedin assays to test for one or more biological activities. If phosphatoninpolynucleotides and polypeptides do exhibit activity in a particularassay, it is likely that phosphatonin may be involved in the diseasesassociated with the biological activity. Therefore, phosphatonin couldbe used to treat the associated disease.

Regulatory sequences of phosphatonin genes

In a further aspect the present invention relates to a regulatorysequence of a promoter naturally regulating the expression of apolynucleotide encoding the phosphatonin polypeptide of the inventiondescribed above or of a polynucleotide homologous to a polynucleotide ofthe invention. With methods well known in the art it is possible toisolate the regulatory sequences of the promoters that naturallyregulate the expression of the above-described DNA sequences. Forexample, using the above described nucleic acid molecules as probes agenomic library consisting of human genomic DNA cloned into phage orbacterial vectors can be screened by a person skilled in the art. Such alibrary consists e.g. of genomic DNA prepared from human blood cells,fractionized in fragments ranging from 5 kb to 50 kb, cloned into thelambda GEM11 (Promega) phages. Phages hybridizing with the probes can bepurified. From the purified phages DNA can be extracted and sequenced.For example, a human genomic P1 library (Genomic Systems, Inc.) isscreened by a labeled cDNA probe as described in Example 11. Havingisolated the genomic sequences corresponding to the genes encoding theabove-described phosphatonin proteins, it is possible to fuseheterologous DNA sequences to these promoters or their regulatorysequences via transcriptional or translational fusions well known to theperson skilled in the art. In order to identify the regulatory sequencesand specific elements of these phosphatonin genes, 5′-upstream genomicfragments can be cloned in front of marker genes such as luc, gfp or theGUS coding region and the resulting chimeric genes can be transfectedinto cells or animals for transient or stable expression. The expressionpattern observed in the transgenic animals or transfected mammaliancells containing the marker gene under the control of the regulatorysequences of the invention can be compared with that of the phosphatoningene described in Example 10 and reveals the boundaries of the promoterand its regulatory sequences. Usually, said regulatory sequence is partof a recombinant DNA molecule, e.g., a vector see supra. The presentinvention furthermore relates to host cells transformed with aregulatory sequence or a DNA molecule or vector containing theregulatory sequence of the invention. Said host cell may be aprokaryotic or eukaryotic cell; see supra.

Diagnosing disorders of phosphate metabolism

Another object of the present invention concerns the pharmacogenomicselection of drugs and prodrugs for patients suffering from disorders inphosphate metabolism (see, e.g., Example 6) and which are possiblecandidates to drug therapy. Thus, the findings of the present inventionprovide the options of development of new drugs for the pharmacologicalintervention with the aim of restituting the function of geneticallymodified phosphatonin proteins. Also a gene therapeutical approach canbe envisaged with the aid of the present invention. Thus, the inventionprovides a diagnostic method of a disorder, which involves:

-   -   (a) assaying phosphatonin gene expression level in cells or body        fluid of an individual; and    -   (b) comparing the phosphatonin gene expression level with a        standard phosphatonin gene expression level, whereby an increase        or decrease in the assayed phosphatonin gene expression level        compared to the standard expression level is indicative of        disorder in phosphate metabolism, e.g., the kidney or bone        system, or other tissues.

More particularly, the present invention relates to a method ofdiagnosing a pathological condition or a susceptibility to apathological condition in a subject related to a disorder of phosphatemetabolism comprising:

-   -   (a) determining the presence or absence of a mutation in the        polynucleotide encoding phosphatonin; and    -   (b) diagnosing a pathological condition or a susceptibility to a        pathological condition based on the presence or absence of said        mutation.

In another embodiment, the present invention relates to a method ofdiagnosing a pathological condition or a susceptibility to apathological condition in a subject related to a disorder of phosphatemetabolism comprising:

-   -   (a) determining the presence or amount of expression of a        phosphatonin polypeptide or a mutant form thereof in a        biological sample; and    -   (b) diagnosing a pathological condition or a susceptibility to a        pathological condition based on the presence or amount of        expression of the polypeptide.

It is evident that the above-described nucleic acid probes andantibodies of the invention are preferably used for the mentionedmethods.

The above described diagnosis method can also be employed to determinethe status of said disorders. In connection with the present invention,the term “pathological condition” include the options that the gene,mRNA, protein or a transcription control element, e.g. promoter/enhancersequence may bear a mutation, deletion or any other modifications whichwould affect the overall activity of the gene when compared to thewild-type normal gene product. Included in this term arepost-translational modifications of the protein.

In a preferred embodiment of the method of the present invention saidstatus in said subject is indicative of a certain form of the disorderin phosphate metabolism. Furthermore, it can be advantageous that in themethod of the invention said status in said subject is determined in theembryonic status or in the newborn status, for example usingaminocentesis.

The specific analysis of the status of (potential) disorder of phosphatemetabolism at the embryonic, newborn or adult stage will provide furtherinsights into, e.g., specific disease states associated with therespective stages. For example, it is expected that the etiology of,e.g., X-linked Hypophosphatemic Rickets (XHL) or OncogenicHypophosphatemic Osteomalacia (OHO) will be elucidated by applying themethods of the present invention. Upon the basis of this knowledge, newpharmaceutical active drugs will be developed and tested. The method ofthe invention can also be applied to a variety of animals, depending onthe purpose of the investigation. Thus, in a preferred embodiment, theanimal is a mouse. This embodiment is particularly useful for basicresearch to understand more clearly the functional interrelationship ofdifferent proteins which regulate the phosphate metabolism. In a furtherembodiment the animal is a human. In this embodiment, preferablydiagnostic and therapeutic applications are envisaged.

In a preferred embodiment of the above-described method a further stepcomprising treating said newborn with a medicament to abolish oralleviate a disorder in phosphate metabolism is performed. Earlydiagnosis of a disorder in phosphate metabolism or susceptibility tothis disorder is particularly advantageous and of considerable medicalimportance. This preferred embodiment can be used to diagnose the statusin, e.g., the coronar villi, i.e. prior to the implantation of theembryo. Furthermore, the status can, with the method of the presentinvention, be diagnosed via amniocentesis. The early diagnosis ofdisorders in the phosphate uptake and/or reabsorption in accordance withall applications of the method of the invention allows treatmentdirectly after birth before the onset of clinical symptoms.

X-linked rickets patients and tumour osteomalacia patients (prior totumour resection, or if resection is not possible), are treated withhigh doses of calcitriol or 1,25 dihydroxy vitamin D₃ (also knowncommercially as Rocaltrol^(R) and is available from Roche; see web sitefor detailed information on administrationhttp://www.rochecanada.com/rocaltrol pml e.html. and oral phosphatesupplements (dibasic sodium phosphate and/or phosphoric acid). Vitamin Danalogs are also occasionally used (e.g., dihydrotachysterol), andurinary loss of phosphorus and calcium is reported to be further reducedby the additional use of thiazide diuretics such as hydrochlorothiazideand amiloride (Alon, Paediatrics 75 (1985), 754-763). For an extensivereview of current treatments refer to (Carpenter, Pediatric Clinics ofNorth America 44 (1997), 443-466). In children bones need to be reset bybreaking deformed limbs (osteotomy), and the medications described aboveresult in severe vomiting and diarrhea. Growth defects associated withfamilial rickets cannot be satisfactorily addressed using currenttreatments.

Replacing the above medications with phosphatonin and/orphosphatonin-peptide derivatives would correct the clinical symptoms andnormalize the growth defects without the unpleasant side effects andsurgical osteotomies.

In another preferred embodiment of the above-described methods, saidmethods further comprise introducing the functional and expressiblephosphatonin gene into cells of a subject having a disorder orsusceptibility to a disorder in phosphate metabolism. In this contextand as used throughout this specification, “functional” phosphatoningene means a gene wherein the encoded protein having part or all of theprimary structural conformation of the phosphatonin polypeptidepossessing the biological activity described above. The detection of anexpression of a mutant form of phosphatonin would allow the conclusionthat said expression is interrelated to the generation or maintenance ofa disorder in phosphate metabolism. Accordingly, one alternative oradditional step would be applied to reduce the expression level to lowlevels of the mutant phosphatonin or abolish the same. This can be done,for example, by at least partial elimination of the expression of themutant gene by biological means, for example, by the use of ribozymes,antisense nucleic acid molecules or intracellular antibodies against themutant forms of these proteins. Furthermore, pharmaceutical products maybe developed that reduce the expression levels of the correspondingmutant genes.

Binding activity

In a further aspect the present invention relates to a method foridentifying a binding partner to a phosphatonin polypeptide comprising:

-   -   (a) contacting a phosphatonin polypeptide of the invention with        a compound to be screened; and    -   (b) determining whether the compound effects an activity of the        polypeptide.

Phosphatonin polypeptides may be used to screen for proteins that bindto phosphatonin or for proteins to which phosphatonin binds. The bindingof phosphatonin and the molecule may activate (agonist), increase,inhibit (antagonist), or decrease activity of the phosphatonin or themolecule bound. Examples of such molecules include antibodies,oligonucleotides, proteins (e.g., receptors), or small molecules.

Preferably, the molecule is closely related to the natural ligand ofphosphatonin, e.g., a fragment of the ligand, or a natural substrate, aligand, a structural or functional mimetic; see, e.g., Coligan, CurrentProtocols in Immunology 1(2) (1991); Chapter 5. Similarly, the moleculecan be closely related to the natural receptor to which phosphatoninbinds, or at least, a fragment of the receptor capable of being bound byphosphatonin (e.g., active site). In either case, the molecule can berationally designed using known techniques; see also supra.

Preferably, the screening for these molecules involves producingappropriate cells which express phosphatonin, either as a secretedprotein or on the cell membrane. Preferred cells include cells frommammals, yeast, Drosophila, or E. coli. Cells expressing phosphatonin(or cell membrane containing the expressed polypeptide) are thenpreferably contacted with a test compound potentially containing themolecule to observe binding, stimulation, or inhibition of activity ofeither phosphatonin or the molecule.

The assay may simply test binding of a candidate compound tophosphatonin, wherein binding is detected by a label, or in an assayinvolving competition with a labeled competitor. Further, the assay maytest whether the candidate compound results in a signal generated bybinding to phosphatonin.

Alternatively, the assay can be carried out using cell-freepreparations, polypeptide/molecule affixed to a solid support, chemicallibraries, or natural product mixtures. The assay may also simplycomprise the steps of mixing a candidate compound with a solutioncontaining phosphatonin, measuring phosphatonin/molecule activity orbinding, and comparing the phosphatonin/molecule activity or binding toa standard.

Preferably, an ELISA assay can measure phosphatonin level or activity ina sample (e.g., biological sample) using a monoclonal or polyclonalantibody. The antibody can measure phosphatonin level or activity byeither binding, directly or indirectly, to phosphatonin or by competingwith phosphatonin for a substrate.

All of these above assays can be used as diagnostic or prognosticmarkers. The molecules discovered using these assays can be used totreat disease or to bring about a particular result in a patient (e.g.,increase of phosphate level in the blood) by activating or inhibitingthe phosphatonin/molecule. Moreover, the assays can discover agentswhich may inhibit or enhance the production of phosphatonin fromsuitably manipulated cells or tissues.

Therefore, the invention includes a method of identifying compoundswhich bind to phosphatonin comprising the steps of:

-   -   (a) incubating a candidate binding compound with phosphatonin;        and    -   (b) determining if binding has occurred.

Moreover, the invention includes a method of identifyingagonists/antagonists comprising the steps of:

-   -   (a) incubating a candidate compound with phosphatonin;    -   (b) assaying a biological activity as described above, and    -   (c) determining if a biological activity of phosphatonin has        been altered.

As mentioned hereinbefore, the polynucleotides and polypeptides of thepresent invention provide a basis for the development of mimeticcompounds that may be inhibitors or activators of phosphatonin or theirencoding genes. It will be appreciated that the present invention alsoprovides cell based screening methods that allow ahigh-throughput-screening (HTS) of compounds that may be candidates forsuch inhibitors and activators.

In a further embodiment, the present invention relates to a method ofidentifying and obtaining a drug candidate for therapy of disorders inphosphate metabolism comprising the steps of

-   -   (a) contacting the polypeptide of the present invention or a        cell expressing said polypeptide in the presence of components        capable of providing a detectable signal in response to        phosphate uptake, with said drug candidate to be screened under        conditions to permit phosphate metabolism, and    -   (b) detecting presence or absence of a signal or increase of the        signal generated from phosphate metabolism, wherein the presence        or increase of the signal is indicative for a putative drug.

For example, renal cell line CL8, human primary renal cells, or primaryhuman osteoblast cells can be used to measure radioactive Na⁺-dependentphosphate uptake and/or vitamin D metabolism using methods described by,e.g., Rowe, 1996; supra.

Furthermore, poly A+ RNA or total RNA extracted from cells described in(a), and oligonucleotide primers complementary to sequence for phosphatetransporter genes (NPTII etc), renal 24-hydroxylase, a α hydroxylase,PTH, or osteopontin to measure expression of these genes using, e.g.,the polymerase chain reaction can be employed.

In addition, the measurement of mineralization of human primaryosteoblast cells using von kossa stain is feasible. This methodcomprises, for example,

-   -   growing human primary-osteoblasts (obtainable from        Clonetics-Biowhitaker) to confluence using media supplements and        conditions recommended by Clonetics;    -   for mineralization experiments supplementing the cells with        phosphate donor β-glycerphosphate, and for controls        hydrocortisone-11-hemisuccinate;    -   supplementing experimental cells with β-glycerphosphate and MERE        25 ng/ml;    -   After 3 weeks in culture and serial changes of media staining        the osteoblasts for bone mineralization using the Von-Kossa        stain as described by Clonetics (AgNO₃; silver salt        precipitation).    -   Furthermore, assays comprising the following measures can be        employed:    -   Rat perfusion experiments and measuring effects of phosphatonin        on renal phosphate uptake;    -   determining the expression of a range of relevant genes in        human-renal cell line CL8 and the effects of MEPE        supplementation, such as:    -   Na+ Phosphate transporters,    -   24 and 1-αhydroxylase,    -   Osteopontin and osteocalcin;    -   co-transfection system in COS cells with MEPE and PHEX;    -   Bio-assay studies using peptide fragments comprising at least        one of the above described motifs. Hence, another detection        method comprises the measurement of protein kinase C, casein        kinase II, tyrosines kinase or other signal transduction        pathways in cells exposed to phosphatonin and derivative        peptides using contemporary techniques. Furthermore, the methods        as described in the appended examples can be easily adapted to        the above-described screening methods.

The drug candidate may be a single compound or a plurality of compounds.The term “plurality of compounds” in a method of the invention is to beunderstood as a plurality of substances which may or may not beidentical.

Said compound or plurality of compounds may be chemically synthesized ormicrobiologically produced and/or comprised in, for example, samples,e.g., cell extracts from, e.g., plants, animals or microorganisms.Furthermore, said compound(s) may be known in the art but hitherto notknown to be capable of suppressing or activating phosphatoninpolypeptides or other components in the phosphate metabolism. Thereaction mixture may be a cell free extract or may comprise a cell ortissue culture. Suitable set ups for the method of the invention areknown to the person skilled in the art and are, for example, generallydescribed in Alberts et al., Molecular Biology of the Cell, thirdedition (1994) and in the appended examples. The plurality of compoundsmay be, e.g., added to the reaction mixture, culture medium, injectedinto a cell or otherwise applied to the transgenic animal. The cell ortissue that may be employed in the method of the invention preferably isa host cell, mammalian cell or non-human transgenic animal of theinvention described in the embodiments hereinbefore.

If a sample containing a compound or a plurality of compounds isidentified in the method of the invention, then it is either possible toisolate the compound from the original sample identified as containingthe compound capable of suppressing or activating phosphatonin, or onecan further subdivide the original sample, for example, if it consistsof a plurality of different compounds, so as to reduce the number ofdifferent substances per sample and repeat the method with thesubdivisions of the original sample. Depending on the complexity of thesamples, the steps described above can be performed several times,preferably until the sample identified according to the method of theinvention only comprises a limited number of or only one substance(s).Preferably said sample comprises substances of similar chemical and/orphysical properties, and most preferably said substances are identical.

The compounds which can be tested and identified according to a methodof the invention may be expression libraries, e.g., cDNA expressionlibraries, peptides, proteins, nucleic acids, antibodies, small organiccompounds, hormones, peptidomimetics, PNAs or the like (Milner, NatureMedicine 1 (1995), 879-880; Hupp, Cell 83 (1995), 237-245; Gibbs, Cell79 (1994), 193-198 and references cited supra). Furthermore, genesencoding a putative regulator of phosphatonin protein and/or which exerttheir effects up- or downstream the phosphatonin protein of theinvention may be identified using, for example, insertion mutagenesisusing, for example, gene targeting vectors known in the art (see, e.g.,pShooter plasmid series that target expression to the nucleus,mitochondria, or cytoplasm pEF/myc/nuc, pCMV/myc/nuc, pEF/myc/mito,pCMV/myc/mito, pEF/myc/cyto, pCMV/myc/cyto, or pDISPLAY expressionvector that targets recombinant proteins to the surface of mammaliancells. All the vectors are obtainable from Invitrogen(http://www.invitrogen.com/)).

Determining whether a compound is capable of suppressing or activatingphosphatonin proteins can be done, for example, by monitoring Na-dependent phosphate uptake or bone mineralization; see supra. It canfurther be done by monitoring the phenotypic characteristics of the cellof the invention contacted with the compounds and compare it to that ofwild-type cells. In an additional embodiment, said characteristics maybe compared to that of a cell contacted with a compound which is eitherknown to be capable or incapable of suppressing or activatingphosphatonin proteins.

Once the described compound has been identified and obtained, it ispreferably provided in a therapeutically acceptable form. Thus, thepresent invention also relates to a method of producing a therapeuticagent comprising the steps of the methods of the invention describedabove; and

-   -   (i) synthesizing the compound obtained or identified in step (b)        of a method of the invention or an analog or derivative thereof        in an amount sufficient to provide said agent in a        therapeutically effective amount to a patient; and/or    -   (ii) combining the compound obtained or identified in step (b)        of a method of the invention or an analog or derivative thereof        with a pharmaceutically acceptable carrier

Methods for the preparation of chemical derivatives and analogues arewell known to those skilled in the art and are described in, forexample, Beilstein, Handbook of Organic Chemistry, Springer edition NewYork Inc., 175 Fifth Avenue, New York, N.Y. 10010 U.S.A. and OrganicSynthesis, Wiley, N.Y., USA. Furthermore, said derivatives and analoguescan be synthesized and tested for their effects according to methodsknown in the art; see also supra and infra.

In summary, the present invention provides methods for identifyingcompounds which are capable of modulating phosphate metabolism due totheir direct or indirect activation or phosphatonin. Accordinglycompounds identified in accordance with the method of the presentinvention to be inhibitors and activators, respectively, of phosphatoninactivity are also within the scope of the present invention.

As is evident from the above, the present invention generally relates tocompositions comprising at least one of the aforementionedpolynucleotides, nucleic acid molecules, vectors, proteins, regulatorysequences, recombinant DNA molecules, antibodies or compounds.Preferably, said composition comprises ingredients such as buffers,cryoprotectants etc. which are not naturally associated with thementioned components of the invention and render the same suitable for aparticular use.

Advantageously, said composition is for use as a medicament, adiagnostic means or a kit. Pharmaceutical compositions are described inmore detail in Examples 6 and 7. In particular, bioactive fragments asdescribed above may be useful as a medicament in the treatment of adisorder of phosphate metabolism such as X-linked rickets andosteomalacia as well as other diseases of bone mineral metabolism. Thereis further provided phosphatonin and PHEX metallopeptidase as a combinedpreparation for simultaneous, separate or sequential use as amedicament. In this way, the PHEX metallopeptidase may be used to cleavephosphatonin so as to produce active phosphatonin fragments which may beused for the treatment of disorders of phosphate metabolism as discussedherein. Whilst all of these diseases are particularly important inhumans, other mammals may also be treated in accordance with theinvention.

The present invention has provided for the first time phosphatonin in asubstantially isolated or purified form which is suitably free ofcontaminants. Native phosphatonin and native fragments of phosphatonin,which are free of contaminants such as SDS and/or other interferingproteins are capable of regulating phosphate metabolism and of providingactive ingredients in pharmaceutical compositions for the treatment ofdiseases associated with disorders of phosphate metabolism.

Hence, the present invention relates to the use of a phosphatoninpolypeptide of the present invention or a DMA encoding and capableexpressing said polypeptide, the antibody, the activator/agonist,inhibitor/antagonist or binding partner of the present invention, forthe preparation of a medicament for treatment of a disorder of phosphatemetabolism.

In particular, the present invention relates to the use of aphosphatonin polypeptide having phosphatonin activity or a DMA encodingand capable expressing said polypeptide, the antibody, theactivator/agonist or binding partner of the invention whose presence inthe cell leads to phosphatonin activity, for the preparation of amedicament for the treatment of hyperphosphatemia, preferably for thetreatment of renal osteodystrophy, hyperphosphatemia in renaldialysis/pre-dialysis, secondary hyperparathyrodism or osteitis fibrosacystica.

In another embodiment, the present invention relates to the use of aphosphatonin polypeptide having anti-phosphatonin activity or a DNAencoding and capable expressing said polypeptide, the antibody of theinvention, the nucleic acid molecule or the inhibitor/antagonist of thepresent invention, for the preparation of a medicament for the treatmentof hypophosphatemia, preferably for the preparation of a medicament forthe treatment of X-linked hypophosphatemic rickets, hereditaryhypophosphatemic rickets with hypercalcuria (HHRH), hypomineralized bonelesions, stunted growth in juveniles, oncogenic hypophosphatemicosteomalacia, renal phosphate leakage, renal osteodystrophy,osteoporosis, vitamin D resistant rickets, end organ resistance, renalFanconi syndrome, autosomal rickets, Paget's disease, kidney failure,renal tubular acidosis, cystic fibrosis or sprue.

In a preferred embodiment of the present invention, the phosphatoninpolypeptide having anti-phosphatonin activity or a DNA encoding andcapable expressing said polypeptide, the antibody of the invention, thenucleic acid molecule of the invention or the inhibitor/antagonist ofthe invention are used for the manufacture of a medicament for thetreatment of a bone mineral loss disorder.

In another preferred embodiment, the present invention relates to theuse of a phosphatonin polypeptide and PHEX metallopeptidase for themanufacture of a combined preparation for simultaneous, separate orsequential use for the treatment of a disorder of phosphate metabolism.

The above-mentioned uses and methods are described in more detail inExample 6.

In another embodiment, the present invention relates to the use of atransformed osteoblast or bone cell line capable of phosphatoninoverexpression for the production and isolation of phosphatonin.

The following examples are put forth so as to provide those skilled inthe art with a complete disclosure and description of how to carry outvarious aspects of the invention and are not intended to limit the scopeof what the inventors regard as their invention, nor are they intendedto represent or imply that the experiments below are all of or the onlyexperiments performed. Efforts have been made to ensure accuracy withrespect to numbers used (e.g., amounts, temperatures, etc.) but someexperimental error and deviation should be accounted for. Unlessindicated otherwise parts are parts by weight, molecular weight isweight average molecular weight and temperature is in degreescentigrade.

EXAMPLE 1

Purification of Phosphatonin from Tumor

A mesenchymal tumor with phosphaturic expression was removed from apatient and the following samples taken:

-   -   A: Sample of pure tumor tissue, size of two large peas, was        placed into a 2 ml vial containing DMEM        Eagles/10%FCS/glutamine/antibiotic antimycotic Gibco-BRL    -   B: Sample of sub-dura tumor approximately the same size possibly        smaller. Placed in same media as A.    -   C: Sample of abnormal dura: tough white material: Placed in same        media as A.    -   D: Sample of tumor fluid.        Processing of Samples:

Day 1:

The samples were each cut into small 0.5 cm cubes using a sterilescalpel. Half of each sample was placed into a cryotube and frozen downin N2(l) immediately. The fluid surrounding the tissue (DMEM/10% FCSetc.), was also collected and frozen down. The other half of each samplewas added to DMEM Eagles/10% FCS/glutamine/antimycotic antibioticsupplemented with collagenase Al 0.2mg/ml (˜15ml), and left at 37° C.overnight.

Day 2:

1. After overnight incubation in serum supplemented DMEM, the cellsappeared to be predominantly RBC's and very few adherent cells wereobserved. The cells were spun down at room temp and the supernatantscollected and immediately frozen down (˜15 ml).

2. The pellets were then resuspended in 10 ml of DMEM Eaglessupplemented with antibiotic/antimycotic (medium flasks), and thenincubated for a further 8h 10 min.

3. The serum-free supernatants were collected as described in 1 (˜10ml), and the cells were resuspended in DMEM EAGs with 10% FCS etc., (˜15ml), and incubation continued. The supernatants were stored at −80° C.

Day 6:

1. After incubation from Day 2, cells were spun down as described for 1of Day 2. 10% PCS samples were collected and frozen.

2. Pellets were resuspended in serum free DMEM (10 ml), as for Day 2 andthis time left for four hours.

3. Same as for 3 of Day 2.

Day 7:

1. The subdura and tumor culture in particular, had developedinnumerable foci containing clumps of cells which appeared attached tothe plastic of the tissue culture plates. Underneath these polyp likeprotuberances was a monolayer of fibroblast like cells which spread outradially from underneath the tumor like structures. This layer of cellsappeared to act as a matrix to anchor the polyp like tumors. None ofthis was seen in the dura sample, which appeared to lack cells at thisstage, and contained fibrous like matted structures.

2. Cultures were spun down, and the supernatants collected (10% FCS).The pellets were then placed to one side.

3. The plates were then incubated with 10 ml of trypsin EDTA solnGibco/BRL 1/10 dilution in PBS for ˜15 min. Plates were then tappedvigorously and 5 ml of FCS added.

4. The resuspended cells were then added to the pellets obtained in 2,resuspended and spun down. The supernatant was discarded.

5. Cells were then plated out in 18 ml of 10% FCS DMEM Eagles mediumwith glutamine and antibiotic antimycotic supplements (large flakes wereused.)

6. Finally cells were incubated at 37° C. in CO₂ atmosphere.

Day 9:

1. Tumor cells and to some extent the subdura cells appeared asinnumerable clumps of cells, and appeared to have the same morphology asthe cells prior to trypsin treatment. Some of the clumps were quitelarge, and visible to the naked eye.

2. The serum supplemented media was collected and stored down. Largeflasks were used and 18 ml of media per flask added (DMEM 10% FCSantimycotic/antibiotic/glutamine).

Day 13:

1. Cells were frozen down (˜15 ml), and stored in falcons as 10% FCSDMEM conditioned media.

2. Cells resuspended in serum free DMEM Eags (˜11 ml) 11.10 am, and leftfor 6 h at 37° C. (CO₂ incubator).

3. Cells were then spun down and the supernatants collected (serum freecontrol media). 10% FCS DMEM EAG was then added to the remaining cells.

Day 16:

The above process was repeated and Tumor Conditioned Medium (TCM)collected over several weeks. Alternatively, TCM may be collected fromSaos-2 cells (ECACC 89050205) or U-2 OS cells (ATCC HTB-96).

Purification of Phosphatonin:

Concanavalin A sepharose affinity chromatography:

1. 3ml of TCM was adjusted with IM sodium phosphate pH 7.2 and 5M NaCIto give a final concentration of 0.06M Sodium phosphate pH 7.2 and 0.5MNaCI plus 0.01% sodium azide.

2. Con A Sepharose (Pharmacia Code No: 17-0440-01), arrived in 20%Ethanol, and this was first washed with several column volumes of water,and then equilibrated in the running buffer. A small C10/10 column(Pharmacia code No:

C10/10 id 10 mm), was packed with Con A to a height of 5.5 cm (approx.volume 4.3 to 5.0 ml). Equilibration was carried out at max flow rate of0.5 ml/min.

3. The sample (adjusted to pH 7.2 sodium phosphate/0.5M NaCI 70.01%sodium azide), was then added to the column by gravity feed, andreloaded three times. The color of the sample enabled visualization ofthe passage through the column. Unbound material was then collected andstored for future reference.

4. Waters LC system was then connected and the sample was washed withseveral column volumes of loading buffer.

5. After loading and washing, elution was carried out using sodiumphosphate buffer 60 mM pH 7.2/0.5M Nacl/0.5Mα-methyl-D-glucopyranoside/0.01% azide buffer. See FIG. 1 a. A singlepeak was detected and this was collected.

6. The column was then run to base line approximately 40 ml max, andthen left overnight.

7. After overnight incubation in methyl glycoside buffer, a second peakwas eluted (see FIG. 1 b), which peaked at ˜5 ml.

8. The second peak was collected and dialyzed against 0.05M acetic acid,and then lyophilized. Both Concanavalin peaks A1 (low affinity), andconcanavalin A2 (high affinity), are potent at inhibiting Na+ dependentphosphate co-transport and vitamin D metabolism in a human renal cellline (CL8). The high affinity fraction, the human renal cell line (CL8),and the conditions used for assay are described in Rowe et al 1996. Afurther suitable known renal cell line for this assay is the OK cellline deposited as ECACC 91021202.

Cation exchange Chromatography using HIT rap SP cation exchange 1 mlcolumn (Code No 17-1151-01: Pharmacia):

1. The lyophilized protein was then re-dissolved in 0.05M ammoniumacetate pH 5 and the applied to an equilibrated 1 ml HiTrap SP sepharosecation exchange column.

2. The column was equilibrated prior to sample addition by washing withwater, and then 5 volumes of start buffer (0.02 M ammonium acetate pH5).

3. Sample was eluted using the following protocol; % NH⁴ % NH⁴ Time Flowrate acetate acetate/0.5 M Num min ml/min pH5 NaCl pH5 1 0.5 100 0 2 150.5 25 75 3 20 0.5 0 100 4 25 0.5 0 100 5 35 0.5 100 0 6 50 0.5 100 0

A Single sharp peak was obtained, and the sample was then dialyzedagainst 0.05M acetic acid and lyophilized; see FIG. 2.

After resuspending in 10 mM phosphate buffer pH 7.2 20 μl, aliquots wereresuspended in SDS-PAGE sample buffer (to a final concentration=125mMTRIS-HCL pH6; 2.5% glycerol; 0.5% w/v SDS: 5% β-mercaptoethanol; 0.01%bromophenol blue), boiled (5 mins), cooled and then run on an SDS PAGEgel 12.5% (see chromatogram), and a double band of 55 kD was resolved(see Rowe et al 1996). Both the Concanavalin A and cation bands alsohave an aggregated form. All fractions including the tumor conditionedmedia were potent at inhibiting Na⁺ dependent phosphate co-transport ina human renal cell line (1/1000 diln), and also altered vitamin Dmetabolism. For a full description of the methods used to measurephosphate transport and vitamin D metabolism see Rowe et al 1996. Allpurification modalities were carried out on a waters HPLC/FPLC systemprogrammed by computer-millennium software. The most active fraction wasthe concanavalin A1 fraction from OHO tumor. Anti pre-operation antiserawas used to screen the immobilized purified fraction. The fraction isalso potent at inhibiting NaPi, and affects vitamin D metabolism in ahuman renal cell line (CL8).

EXAMPLE 2

Screening of tumor conditioned-medium (TCM). and purified fractions withpre/post- operation antisera: plus glvcoprotein screen

Pre-operation and post-operation antisera from a patient has beendescribed previously in Rowe et al 1996. Only pre-operation antiseradetected the purified fractions and hormone in TCM in which Western andglycoprotein detection of TCM and purified fractions was achieved usingenhanced chemiluminescence. Protein markers were biotinylated, andtagged with streptavidin peroxidase conjugate. The arrows show theaggregate and active glycoprotein. Post-operation antisera and rabbitpre-immune sera did not detect any of the fractions. Also, only thosetumors secreting phosphaturic factor were positive. Media and skincontrols were negative. A distinct feature of the Con A1, Con A2 and CA1samples was their potent ability to inhibit NaPi, and alter vitamin Dmetabolism in a human renal cell line (CL8). All the purified fractionshave a tendency to aggregate into a lower mobility form on SDS-PAGE.Also, the purified fractions and TCM active fractions are heavilyglycosylated. The extent of glycosylation was confirmed by periodateoxidation of immobilized proteins on PVDF membranes followed bybiotinylation of carbohydrate moieties. These were then screened withstreptavidin conjugated to horse radish peroxidase and enhancedchemiluminescence. The active form (inhibits NaPi etc.), is associatedwith the 58 to 60 kDa fraction. An additional and powerful way ofpurifying the protein to homogeneity is the use of a neutral pH 7SDS-PAGE system using a 4-12% Bis-Tris Gel with MOPS running buffer.Pre-caste gels can be purchased from Novex.

EXAMPLE 3

SDS-PAGE at neutral pH using 4-12% polyacrylamide gradient and Bis-Trisgel with MOPS running buffer (Nu-PAGE system from NOVEX): Reducedmobility of hormone

On this system a fraction of the glycosylated hormone has a reducedmobility, and runs at ˜200 kDa. The lower molecular weight form is alsovisible at 58/60 kDa. Appearance of the ˜200kDa protein may be due tothe isoelectric point of the protein (different charge at neutral pH),and the interaction of carbohydrate moiety with the gel matrix. Also,increased efficiency of electro-blotting of high molecular weightcomponents occurs due to the low % acrylamide (4-12% gradient), at thetop of the gradient gel. Running fractions through this system increasesthe purity and homogeneity of the molecule. A Western blot using thissystem and including the following samples (pre-operation antiserum wasused to screen the blots using enhanced chemiluminescence detection): 1.protein markers; 2. intracranial tumor cell line OHO; 3. cells fromsub-dura adjacent to tumor; 4. cells from dura adjacent to sub-dura; 5.HTB6 cell line; 6. Saos-2 cell line; 7. defined medium control; 8. Skinfibroblast control; 9. Linear sebaceous naevus polyp tumor demonstratedthat Naevus polyp tumor showed a specific phosphaturic band at ˜200kDaon SDS-PAGE Neutral gels.

EXAMPLE 4

Cloning and Sequencing of Phosphatonin

1. Library construction:

A tumor derived from a patient described in an earlier publication (BD,Rowe et al., 1996), was sectioned and mRNA extracted using standardtechniques. The mRNA was copied using reverse transcriptase to generatea cDNA population that was then subsequently subcloned into abacteriophage vector λ-ZAP II uni (vector purchased from StratageneLtd., Unit 140, Cambridge Science Park, Milton Road, Cambridge, CB4 4GFUnited Kingdom). The cloning was uni-directional and the 5′ end of thegene was adjacent to the T3 promoter and abutted an EcoRI site. The 3′end of the cDNA's abutted an Xho-1 site upstream of a bacterial T7promoter. Briefly, resected tumour from patient BD was cut into 1 mmblocks and poly A+RNA extracted directly using Streptavidin-Magnesphereparamagnetic particle technology (PolyATract^(R) system Promega). Thepurified mRNA was then used to generate a cDNA template using the cDNAsynthesis kit from Stratagene.

Linker primers were added to the cDNA to generate a 5′ EcoRI compatiblecDNA end, and an Xhol compatible 3′ cDNA end, to facilitate forcedorientation cloning into λZAP II uni bacteriophage vector. Recombinantbacteriophages were plated out and amplified on E. coli XL1-Blue mrf′.Total primary clones numbered 800000 with 6% wild type representation.

2. Screening with ore-operative antisera:

The cDNA bacteriophage library was plated out of NZY agar plates and the(3-galactosidase operon induced using IPTG. Expressed fusion proteinswere then transferred to hybond-C membranes (Amersham) and the membraneswere then screened with pre-operation antisera from the patient. Theantisera used has been described (Rowe et a/., 1996). Prior to use theantisera was extensively pre-absorbed with E. coli lysate, and wholeblood to reduce signal to noise. Rabbit antisera raised against patientBD pre-operation serum (Rowe, Bone 18 (1996), 159-169), was extensivelypre-absorbed with normal human serum and E. coli lysate in order toremove E. coli antibodies and background human-serum derived antibodies.Briefly, five 80 mm diameter nitrocellulose filters were added to wholeE. coli lysate (Stratagene), and a second set of five filters weresoaked with normal human serum (10 ml). The impregnated filters wereeach incubated for 10 min at room temperature in sequence with 250 ml of1:1000 diluted anti rabbit pre-operation antisera in 1% BSA; 20 mMTris-HCI (pH7.5), 150 mM NaCI (TBS); 0.02% NaN₃. The preabsorbedpre-operation antisera (pre-Aanti-op) was then used to screen the cDNAlibrary. Bacteriophage λZAP II uni OHO cDNA-clones were plated out on E.coli XL1-Blue mrf and incubated for 3 hours at 37° C. Hybond N⁺ filterspreincubated with 10 mM IPTG were then placed on top of the developingplaques and incubated a further 3 h at 42° C. Filters were then removedand washed with TBS supplemented with Tween 20 (TBST), and then blockedwith 1% BSA in TBS with 0.02% NaN₃ overnight at 4° C. Pre-Aanti-op wasthen added to the blocked filters and left for 1 h at room temperature.Subsequent washes of the filters and incubation with goat-anti-rabbitalkaline phosphatase conjugate, followed by visualization using5-bromo-4-chloro-3-indolyl phosphate/nitroblue tetrazolium was asdescribed by Stratagenes picoblue™ immunoscreening kit. After screening˜600,000 clones, nine positives were selected and purified by secondaryand tertiary screening. The bacteriophage clones were rescued asphagemids using ExAssist helper phage and cloned into E. coli SOLRcells. ExAssist helper phage and SOLR cells were purchased fromStratagene Ltd., Suite 140, Cambridge Science Park, Milton Road,Cambridge, CB4 4GF, United Kingdom.

3. Sequencing clone:

Phagemids were prepared and the DNA sequenced. All nine clones weresequenced. Positive bacteriophage-plaques were removed from agaroseplates after tertiary screening with a sterile hollow quill. The agaroseplugs containing the lytic plaques was then added to 0.5 ml of SM buffersupplemented with 0.02% chloroform, and left at 4° C. overnight. Rescueand transformation of bacteriophage clones to BSCPT SKII phagemids wascarried out using ExAssist phage as described by Stratagene. The hostcells for the purified phagemid were E. coli SOLR cells. Plasmid DNA wasthen prepared using standard techniques (Rowe, Nucleic Acids Res. 22(1994), 5134-5136), and sequenced using ABI fluorescent automatedsequencing and standard vector specific primers. Six of the clones wereoverlapping and in frame with the bacterial β-galactosidase promoter togive contiguous/overlapping epitopes and expressed proteins withidentical overlapping DNA sequences. The longest sequenced cloneencompassed the cDNA sequences of the five others and is shown in FIG.8. This sequence (amino acid/cDNA) is a complete sequence forphosphatonin. There are 430 amino acid residues cloned (SEQ ID NO: 2)and 1655 bp of DNA sequence (SEQ ID NO: 1). Secondary structureprediction indicates a highly hydrophilic protein with glycosylation atthe COOH end, and the presence of a cell attachment tripeptide at theamino end (RGD), see FIG. 8. The protein is also highly antigenic with anumber of major helical domains (FIG. 10). Extensive screening of allavailable databases using BLAST has not revealed any statisticallyrelevant homology to known genes or protein sequences.

4. Purification of recombinant human phosphatonin:

The isolated cDNA clone is represented as rescued phagemids in BscptSKII-vector (Stratagene vector), and contained within SOLR E. coli hostcells. Low level fusion protein expression via induction of theβ-galactosidase promoter by IPTG has been achieved. The phosphatoninclone fusion-product reacts with pre-operation antisera on westernblots. Increased expression and bioactivity of the fusion proteins canbe achieved by sub-cloning into the pCAL-n-EK vector (Stratagene vector)(see below). The construct containing human phosphatonin is contained inE. coli (BL21 ( DE3) pLysS) cells (purchased from Stratagene). IPTGinduction of fusion protein is much higher, and essentially pure proteincan be obtained by calmodulin affinity-chromatography of cell lysates.Recombinant phosphatonin with fusion-tag binds to the calmodulin resinin the presence of Ca²⁺. Phosphatonin fusion protein is then releasedafter washing with EGTA. The small microbial fusion-tag is removed bytreatment with enterokinase, leaving pure human phosphatonin.

4a. Subcloning Phosphatonin into pCAL-n-EK vector

The entire deduced cDNA coding sequence (deduced from the largest cDNAclone pOHO11.1), of phosphatonin (MEPE) was subcloned into theprokaryote expression vector plasmid pCAL-n-EK (Stratagene vector), andthe construct transformed into E. coli BL2 1 (DE3) pLysS and E. coli XL1-Blue mrf′ respectively (strains obtained from Stratagene). The methodof ligation independent cloning (LIC) was used as described byStratagene Affinity™ cloning and protein purification kit (cat No:#214405 and #214407). Two primers were designed from the phosphatoninsequence 5′ and 3′ end respectively with additional overhang linkersequence as follows (bold sequence represents linker): Forward5′GACGACGACAAG.GTGAATAAAGAATATAGTATCAGTAA 3′ (SEQ ID NO: 8)   LinkerReverse 5′GGAACAAGACCCGT.CTAGTCACCATCGCTCTCACT 3′ (SEQ ID NO: 9)  Linker

PCR amplification of phosphatonin includes DMA sequence coding for thefirst valine residue to the stop codon of phosphatonin (see FIG. 8),plus linker sequence. A 5′ overhang of the linker sequence is thengenerated by treating the PCR fragment with Pfu polymerase and dATP.Induction of fusion protein is carried by growing the cells and addingIPTG. The PCR conditions were as follows. Predenaturation; 95° C. 3min,followed by 20 cycles of Denaturation; 95° C. 45 sec, Annealing 59° C.60 sec, 72° C. 2 min, and then 72° C. 7 min final extension; followed bycooling 4° C. A Perkin Elmer 9600 thermocycler was programmed to carryout the PCR, and the following PCR buffer (PB), was used: 10 mM Tris-HCIpH 8, 50 mM KCI, 1 μM primers, 200 jiM dNTP's. PB buffer wassupplemented with 2 mM MgCI2. For ligation independent cloning (LIC),the amplified product was then treated with pfu polymerase and dATP asdescribed by Stratagene, and then directly annealed to linearizedpCAL-n-EK plasmid vector with complementary linker overhangs. Theconstruct was then transformed into competent E. coli XL1-blue mrfcells, and competent E. coli BL21 (DE3) Clones were then selected onampicillin plates, and plasmids prepared and sequenced. A summary of thevector and fusion construct is shown in FIG. 14. High copy numberplasmid is achieved with E. coli XL 1-blue mrf host, and highrecombinant protein expression is obtained with E. coli BL21 (DE3).

4b. Purifying phosphatonin by calmodulin affinity resin

The method as described by Stratagene (cat˜214405), can be used.Sequence upstream from the phosphatonin specific residues will contain acalmodulin binding sequence. Calmodulin resin is added to the crude celllysate in the presence of calcium, and the protein allowed to bind. Theslurry is then washed with calcium containing buffer, and thephosphatonin fusion protein eluted by addition of EGTA 2 mM in a Trisbuffer (50 mM Tris-HCI pH 8). Removal of the calmodulin binding proteintag is then accomplished by digestion with site-specific protease EK,leaving pure recombinant human phosphatonin. Preferably, the method maybe performed as follows (See table below for buffer compositions):

1. Cells are cultured and induced as described by the Stratageneprotocol for pCAL-n-EK vectors (Cat No: #214405), using BL23 (DE3) E.coli host cells comprising plasmid p1BL21; see FIG. 14.

2. Protein lysate is also prepared as described by the Stratageneprotocol but using CCBB-II as resuspension buffer (resuspend cell pelletfrom 500 ml in 10 ml of CCBB-II). It is essential to sonicate in 30 secpulses followed by 4 min cooling with ice. Tubes containing cells arekept on ice during sonication.

3. After sonication cells are spun at 10000 g and the supematantdecanted. Most of the recombinant MEPE remains in the supernatant(protein-lysate).

4. The protein-lysate is then concentrated by using a VIVASCIENCEVIVASPIN (Cat No: VS1521 called 30,000 MWCO PES) concentrator with a30000 molecular weight cut off. Approximately 8 ml of supernatant from500 ml of cells concentrates down to 3.2 ml (X2.5 cone). Furtherconcentration is not advisable.

5. For protein-lysate prepared from 190-200 ml of cells (˜1.3 ml ofequivalent protein-lysate), 1 ml of equilibrated calmodulin resin isthen added (equilibrate resin as described by Stratagene using CCBB-IIbuffer).

6. The suspension is rotated overnight at 4° C.

7. The suspension is spun down (˜3000 rpm on eppendorf centrifuge for 2min), the supernatant removed and the resin resuspended in 1 ml ofCCBB-II buffer.

8. The resin is spun down again and the first wash removed. This isrepeated twice more (total of three washes in CCBB-II).

9. It is then washed once with WB-III; note non of the buffers includingthe final wash buffer contain detergents. The cells used for bio-assayare extremely sensitive to detergents even in trace amounts. WB-III isthe same as CCBB-II but without protease inhibitors.

10. Non-specific proteins are eluted by washing with buffer EB-I twice(1 ml).

11. MEPE is eluted with EB-II 2-3 times (1 ml).

12. Protein is concentrated using a flowgen 10K microsep concentrator at4° C. Generally 3 ml of MEPE eluate can be concentrated down to ˜170 μlin 2 hr.

13. After running samples on an SDS-PAGE gel to assess purity andquantity multiple aliquots are made and frozen at ˜80° C. Repeatedfreeze thaw is avoided.

Buffers: Component CCBB-II WBIII EBI EBII Tris-Buffer pH8  50 mM  50 mM 50 mM 50 mM NaCl 300 mM 300 mM 150 mM  1 M MgAcetate  1 mM  0  0  0Imidazole  1 mM  0  0  0 CaCl2  2 mM  2 mM  0  0 Protease Yes No No NoInhibitors w/o EDTA EGTA  0  0  4 mM  4 mM

Protease inhibitor tablets were added 1 per 10 ml when used (BoehringerMannheim), protease inhibitor w/o EDTA (Cat No: 1836 170). A finalelution with 1M NaCI, EGTA (4 mM) buffer results in >95% purity ofphosphatonin.

EXAMPLE 5

Structure of phosphatonin

1. Primary structure and motifs:

The primary structure of the protein and the nucleic acid sequence areshown in FIG. 8. The largest cDNA clone isolated for MEPE was 1655 bpand contained the entire 3′ end of the gene with poly A⁺ tail and asingle polyadenylation sequence (AA[T/U]AAA) (FIG. 8). An open readingframe of 430 residues was found that overlapped and extended the othersmaller MEPE cDNA clones isolated, with a predicted Mr 47.3 kDa and a plof 7.4. The best fit consensus start codon Kozak, Nucleic Acids. Res. 15(1987), 8125-8148), occurs at 255 bp, although two other methioninespreceded this. It is possible that additional 5′ sequence is missing,and an earlier start codon and or extended 5′ untranslated sequenceneeds to be characterized. GCG- secondary structure prediction indicatesthat the protein is very hydrophilic with three localized areas of lowhydrophobicity (FIG. 9). The protein has glycosylation motifs atresidues 382 and 385 (NNST), and residues 383-386 (NSTR). There is alsoa glycosaminoglycan attachment site at residues 161-164 (SGDG). Theapproximate molecular weight without glycosylation is 54 kDa, and is inclose agreement with the purified glycosylated form of (58-60 kDa).There are a number of phosphorylation site motifs (see Table 1), andthese are predicted to play a role in the biological activity of thehormone or fragments thereof. TABLE 1 Site (on FIG. 8) Motif Protein 8-10 SNK Kinase C phosphorylation 77-79 TPR 118-120 THR 203-205 TKK228-230 TAK 311-313 STR 312-314 TRK 319-321 SNR 384-386 STR 403-405 SNR408-410 SSR 409-411 SRR Casein  8-11 SNKE Kinase II phosphorylation139-142 SDFE 177-180 TGPD 194-197 SEAE 199-202 THLD 224-227 TRDE 228-231TAKE 238-241 SLVE 325-328 TLNE 423-426 SSSE 425-428 SESD 427-430 SDGDCAMP- & 405-408 RRFS cGMP-dependent protein kinase phosphorylationTyrosine Kinase 40-47 KLHDQEEY phosphorylation Myristoylation 16-21GLRMSI 143-148 GSGYTD 119-224 GNTIGT 266-271 GSQNAH 291-296 GSSDAA315-320 GVDHSN 389-394 GMPQGKHGRK Amidation 370-373 HGRK RGD 152-154 RGDGycosaminoglycan 161-165 SGDG Attach. Site Asu-Glycosylation 382-386NNST 383-387 NSTR

A key feature of the protein is a cell attachment sequence at residues152-154 (RGD). The Arg-Gly-Asp sequence plays a role in receptorinteractions in general, and in fibronectin is essential for cellsurface receptor binding to a specific integrin. More notable is thepresence of this motif in some forms of collagens (bone matrix protein),fibrinogen, vitronectin, von Willebrand factor (VWF), snakedisintegrins, and slime mould discoidins. It is highly probable thatthis part of the phosphatonin is involved in receptor and/or bonemineral matrix interactions. Also these interactions mediate thefollowing:

-   -   1. osteoid mineralization (osteoblasts).    -   2. Na-dependent phosphate co-transporter gene expression        regulation.    -   3. 24 hydroxylase and/or 1 alpha hydroxylase gene expression        regulation (kidney).    -   4. bone and dental mineral matrix interactions and regulation of        mineral deposition via nucleation.

The presence of a glycosaminoglycan attachment sequence at residues 161-164 (SGDG), has important implications concerning bone mineralattachment and interactions. The role of proteoglycans in bone is welldocumented particularly in cell signaling. It is highly probable thatthis part of the molecule is also essential for the above bioactivities(point 1 to 4), and in particular osteoblast mediated mineralization ofosteoid.

The RGD motif is in a region of predicted turn (Gamier predictionAntheprot), and is flanked by two regions of p-sheet (residues 134 to141 and 172 to 178). The predicted sheet structure is in turn flanked bytwo regions of extended α-helix (121 to 132 and 196 to 201). The generalstructural context, predicted turn and presence of the RGD cellattachment sequence is similar to that found in osteopontin. The proteinalso has a number of predicted phosphorylation motifs for protein kinaseC, casein kinase II, tyrosine kinase, and cAMP cGMP-dependent proteinkinase. MERE was also found to have a large number of N-myristoylationsites, and these sites appear to be a feature of RGD containing phosphoglycoproteins (osteopontin, vitronectin, collagen, h-integrin bindingprotein, dentin-sialophosphoprotein, dentin-matrix-protein-1,bone-sialoprotein-II and fibronectin). There is an unusually highcontent of aspartate, serine and glutamate residues (26%), as inosteopontin (37%). Of particular interest is the complete absence ofcysteine residues in MEPE sequence, indicating that cysteine-cysteinedisulphide bridges do not play a role in the secondary structure of thismolecule. Sequence homology to dentin phosphoryn (DPP) was found afterscreening the trembl database with MEPE. A region at the C-terminus ofMEPE has a sequence of aspartate and serine residues (residues 414-427)that are almost identical (80% homology), to a recurring motif found inDPP) (FIGS. 26A and 26B). Physicohemical comparison of the MEPE motif(DDSSESSDSGSSSESD) with the DSP motif (SDSSDSSDSSSSSDSS), increases thehomology to 93%. The MEPE-motif occurs once at the C-terminus in MEPE(residues 414 to 427), whereas the DSP homologue is repeated at DSPresidue positions 686 to 699, 636 to 646, and 663 to 677. Moreover, tworelated sequences DSSDSSDSNSSSDS and DSSDSSDSSNSSDS, also with 80%homology to the MEPE-motif are found in DSP at positions 576 to 589 and800 to 813 respectively. A similar motif with 60% homology(DDSHQSDESHHSDESD), is also found in osteopontin (residues 101 to 116),and a casein kinase II phosphorylation site is contained within theregion of homology (FIG. 12). Skeletal casein kinase II activity isdefective in X-linked rickets (Rifas, loc. cit.). Although theosteopontin MEPE-motif is central and not C-terminal, cleavage ofosteopontin in vivo has been reported and this would generate a peptidewith the MEPE motif placed C-terminal (Smith, J. Biol. Chem. 271 (1996),28485-28491). Additional sequence homology to the C-terminal MEPE-motifis also found in DMA-I at residues 408 to 429 (SSRRRDDSSESSDSGSSSESDG).A graphical presentation of the regional sequence homology of theMEPE-motif in DSSP, DMA-1 and OPN is presented in FIG. 12 as a‘llanview’ statistical plot, and Table 2 presents the sequencesimilarities in alignment. TABLE 2 MEPE versus DSSP Upper sequence MEPE:414 DSSESSDSGSSSES 427 (SEQ ID NO: 7) 686 DSSDSSDSSSSSDS 699 (SEQ ID NO:13) 414 DSSESSDSGSSSES 427 (SEQ ID NO: 7) 633 DSSDSSDSSSSSDS 646 (SEQ IDNO: 13) 413 DDSSESSDSGSSSES 427 (SEQ ID NO: 10) 551 DDSSDSSDSSDSSDS 565(SEQ ID NO: 14) 414 DSSESSDSGSSSES 427 (SEQ ID NO: 7) 576 DSSDSSDSNSSSDS589 (SEQ ID NO: 15) 414 DSSESSDSGSSSES 427 (SEQ ID NO: 7) 663DSSDSSDSSSSSDS 677 (SEQ ID NO: 13) 414 DSSESSDSGSSSES 427 (SEQ ID NO: 7)752 DSSESSDSSNSSDS 765 (SEQ ID NO: 16) 414 DSSESSDSGSSSES 427 (SEQ IDNO: 7) 800 DSSDSSDSSNSSDS 813 (SEQ ID NO: 17) MEPE versus Osteopontin:Upper sequence MEPE 413 DDSSESSDSGSSSESD 428 (SEQ ID NO: 11) 101DDSHQSDESHHSDESD 116 (SEQ ID NO: 18) Osteopontin versus DSSP: Uppersequence Osteopontin 106 SDESHHSDESD 116 (SEQ ID NO: 19) 638 SDSSSSSDSSD648 (SEQ ID NO: 20) 106 SDESHHSDESD 116 (SEQ ID NO: 19) 846 SDSSDSSDSSD857 (SEQ ID NO: 21) 106 SDESHHSDESD 116 (SEQ ID NO: 19) 857 SDSSDSSDSSN878 (SEQ ID NO: 22) MEPE versus DMA-1 MEPE top sequence 408SSRRRDDSSESSDSGSSSESDG 429 (SEQ ID NO: 12) 443 SSRSKEDSN-STESKSSSEEDG463 (SEQ ID NO: 23)

Of interest is the repetitive occurrence of the motif at the C-terminalregion of DSSP or the dentin-phosphoryn portion. A dot-matrixsequence-comparison of MERE against DSSP at high and low stringency isshown in FIG. 13, and this illustrates the repetitive occurrence of theaspartate-serine rich MERE motif in DSSP.

DPP is formed by post-translational cleavage of a much larger protein,dentin sialo-phosphoprotein (DSSP), into two distinct proteins DPP anddentin sialoprotein (DSP). There is considerable sequence homology ofMEPE and osteopontin to the dentin phosphoryn (DPP), part of dentinsiaolo-phosphoprotein (DSSP), with no homology to the dentinsiaolprotein portion of the molecule (DSP) (FIG. 13). Of note is theclose alignment of the RGD motif, casein kinase II phosphorylationmotifs and N-glycosylation sites in both DPP and MEPE (FIG. 13). Also,all the protein kinase C sites associated with DSSP are clustered in theregion of overlap with MEPE (dentin phosphoryn portion), with none foundin the DSP portion of the molecule.

2. Secondary structure:

GCG peptide structure prediction profiles ofhydrophobicity/hydrophilicity, antigenicity, flexibility and cellsurface probability are shown in FIGS. 3 to 6.

These Figures show GCG-peptide structure prediction analysis of theprimary amino acid sequence. Hydrophobicity and hydrophilicity indicesare represented as triangles and ovals respectively. Glycosylationmotifs are represented as circles on stalks at residues 382-386.Glycosylation symbols can been seen more clearly in FIG. 6. Protein turnis indicated by the shape of the line representing primary amino acidsequence. Regions of cc-helix, coil and sheet structure are indicated bylocalized undulations of the line (refer to FIG. 7 for more detail).Computer predictions were made using GCG-software derived from HGMPresource center Cambridge (Rice, 1995) Programme Manual for the EGCGpackage. (Cambridge, CB10 1 RQ, England: Hinxton Hall). A strikingfeature is the lack of Sistine residues and the high degree ofhydrophilicity, with four minor sites with low hydrophobic indices(residues 48-53, 59-70, 82-89, and 234-241). The protein does not have atransmernbranous profile as deduced from a secondary structureprediction using antheorplot software. The protein is also highlyantigenic and flexible (FIGS. 4 and 5). The overall secondary structureprofile is indicative of an extracellular secreted protein, and is inagreement with the proposed function of the molecule. FIG. 7 shows thehelical, sheet structure, turn and coil regions of the phosphatonin.This is based on a prediction using Gamier analysis of the antheplotv2.5e package. The four lines in each section (top to bottom), representhelix, coil, sheet, and turn probability indices of primary amino acidsequence. The graph at the bottom presents the same data in block form.Notable is the high helical content, particularly at the NH2 terminusand also towards the C-terminus, which may have a functional context.

EXAMPLE 6

Medical Uses of Phosphatonin and Phospatonin Fragments

A number of disorders are amenable to treatment using polypeptidesaccording to the present invention.

X-linked rickets (hypophosphatemia) (HYP):

X-linked hypophosphatemic rickets is one of the commonest inheriteddiseases of bone mineral metabolism (Rowe, 1997). Phosphatonin bioactivefragments such as those cleaved by PHEX and the uncleaved hormone willplay a major role in the treatment of the disease. The protein clonedand described herein, is predicted to interact with its cognate receptorin the kidney and cause an inhibition in the expression of a renalNa-dependent phosphate co-transporter (NaPi), and either directly orindirectly up-regulation of a renal 24 hydroxylase. It is also predictedto down regulate expression of renal 1 αhydroxylase(directly/indirectly). After cleavage with PHEX or otherpost-translational modifiers, the peptide fragments derivative of thehormone are predicted to have the opposite bio-function (up-regulationof NaPi, down-regulation of 24 hydroxylase, up regulation of 1 alphahydroxylase). The fragment containing the RGD cell attachment residue(152-154), is predicted to play a role in the receptor interactions,although other peptide derivatives may also mediate receptor ligandinteractions for disparate bioactivities. Also, phosphatonin derivativeswill play an important function in the normalization of thehypomineralised bone lesions. This is predicted to occur by mediatingchanges in the osteoblast mediated mineralization of osteoid, and bycorrecting the aberrant expression/phosphorylation of bone mineralmatrix proteins (osteopontin/osteocalcin). The RGD cell attachmentsequence and also the glycosaminoglycan attachment motif could berequired for the functional nucleation and crystallization ofhydroxyapatite and bone mineral.

Growth impairment is a major feature of HYP, and current treatments areunsuitable. Treatment by administration of phosphatonin-derivedfragments as opposed to inorganic phosphate and vitamin Dsupplementation, may correct this.

Accordingly, among the useful effects of peptide fragments ofphosphatonin are:

1. Correction of hypophosphatemia (NaPi, preferably renal)

2. Normalization of 24-hydroxylase 1 alpha hydroxylase activity (renal).

3. mineralization of bone and bone repair (correction/prevention ofrickets).

4. Complete loss of bone pain symptoms.

5. Correction of stunted growth.

Oncoaenic hvpophosphatemic osteomalacia (OHO):

The clinical profile of OHO is similar to HYP. There is a renalphosphate leak, low circulating levels of 1,25 dihydroxy vitamin D3(calcitriol), elevated alkaline phosphatase, bone hypomineralizationthat in adults is presented as a generalized bone softening(osteomalacia) and low serum phosphate. The pathophysiologies of HYP andOHO clearly overlap. In rickets, the defect is a non functional PHEXgene. However, in OHO it is circulating unprocessed phosphatonin. Thetumours are often difficult to find, and can be extremely difficult anddangerous to resect. Control of phosphate metabolism and bonemineralization is essential when removal of tumour is contra-indicated.Administration of PHEX to patients to cleave hormone is predicted to bedangerous as other circulating hormones and proteins may also beaffected by promiscuous cleavage. Phosphatonin-fragments could insteadbe designed that have high receptor affinity and bioactivity, such thatthey would compete effectively with unprocessed tumour-derivedcirculating hormone.

Other rickets or hypophosphatemic conditions:

There are many causes of rickets besides HYP and OHO, the most commoninvolve abnormalities of vitamin D, but there are causes such ashypophosphatemia, renal tubular acidosis, use of certain medications,sprue, cystic fibrosis etc. Use of fragments of phosphatonin, andphosphatonin itself may be of use in treating these diseases. Some ofthe diseases are briefly discussed below (diseases resulting inhyperphosphatemia are potentially treatable by use of the wholehormone).

Renal transplants and renal osteodystrophy:

A chronic feature of renal transplantation is the development of a renalphosphate leak (hypophosphatemia), and abnormal bone mineralization.Phosphatonin fragments would be effective in treating this without theside-effects associated with current medications.

Osteodystophy (a combination of bone disorders), is usually caused bychronic kidney failure (renal disease). Renal failure will result indeath, unless dialysis is given (end stage renal disease). Therefore,patients with osteodystrophy are usually on dialysis therapy. This bonedisease, which is also referred to as “renal osteodystrophy”, is commonin patients on chronic hemodialysis. Secondary hyperparathyroidismdevelops in most patients with chronic renal failure, and is associatedwith the histologic finding of osteitis fibrosa cystica. The disease ischaracterized by growth failure and severe bone deformities in children,especially the very young. The pathogenesis of renal osteodystrophy isrelated to phosphate retention (hyperphosphatemia), and its effect oncalcium and calcitriol metabolism, in addition to roles played bymetabolic acidosis, cytokines, and degradation of parathyroid hormone.Treatment includes restriction of dietary phosphorous intake, phosphatebinders, and use of active metabolites of vitamin D. In this contextaddition of unprocessed hormone would be a powerful means of controllingphosphate levels, and would lead to bone healing. If receptors forphosphatonin are expressed in a range of tissues as well as the kidney,then the potential for treating patients with end stage renal diseaseexists (i.e. complete loss of kidney function).

Osteoporosis/bone mineral loss:

Post-menopausal women are prone to loss of bone mineral with consequentdamage to the integrity of the skeleton. The cause is unknown but islikely to involve a complex interaction of genetic and environmentalfactors. Current research is focussed on refining statistical models toanalyze multifactorial diseases such as osteoporosis.

The use of phosphatonin-derivative fragment(s) would help in thetreatment of this disease by potentially reversing the bone mineralloss. Moreover, the bioactive peptides could be modified to increasepotency and specificity of action.

Paqets disease of bone:

Pagets disease occurs due to asynchronous bone re-modeling. Bonemineralization (mediated by osteoblasts), and bone resorption (mediatedby osteoclasts), are out of step. Excessive osteoclast resorptiveactivity occurs (predominantly in the early resorptive phase), and bonemarrow is replaced by fibrous tissue and disorganized trabeculae.Although the cause is unknown, administration of peptide derivatives ofphosphatonin may help in the treatment of the disease.

Diseases related to disorders in NaPi in other tissues than kidney:

The sodium dependent phosphate co-transporter (NaPi) is expressed notjust in the kidney but in many other tissues. Three type of NaPi, namelyType I, II, and III have been described thus far and all of them aresaid to be expressed in the kidney. In tissues other than the kidney,Type III is said to be expressed ubiquitously (Murer, Eur. J. Physiol.433 (1997) 379-389; Kavanaugh, Kidney Int. 49 (1996) 956-963) and Type Ihas been confirmed to be expressed in the liver and brain in addition tothe kidney (Hilfiker, PNAS 95 (1998), 14564-14569). On the other hand,Type II had been believed to be expressed only in the proximal tubule ofthe kidney.

Although the proximal tubule of the kidney is known to express all ofthe above three types, it is widely accepted that Type II plays the mostsignificant role in terms of phosphate reabsorption at this site. Thishas been demonstrated by a knockout mouse in which the gene (named Npt2)encoding Type II NaPi was inactivated. The homozygous mutants (Npt2-/-)exhibited increased urinary phosphate excretion, hypophosphatemia,elevation in the serum concentration of 1,25-dihydroxyvitamin D, andother typical symptoms with hereditary hypophosphatemic rickets withhypercalciuria (HHRH) (Beck, PNAS 95 (1998), 5372-5377). Since theregulation of phosphate homeostasis in mammals is largely determined bythe kidney, this result is thought to demonstrate that Type II NaPiplays the most important role in systemic phosphate homeostasis amongall three types. Also, these facts, together with the result from theCL8 cell line experiment in the examples indicate that the NaPi that isregulated by Phosphatonin in the kidney is predominantly the Type II.

One of the major clinical problems with renal failure patients ishyperphosphatemia. There is a significant clinical value if suchexcessive serum phosphate is controlled. Therefore, phosphatonin, itsfragments or derivatives which can downregulate NaPi and reduce serumphosphate level has a major potential value. In progressive renalfailure patients (before so-called end stage renal disease =ESRD),downregulation of NaPi expressing in the kidney by phosphatonin will bevaluable.

However, once these patients become ESRD and the majority of kidneyfunction is lost, phosphatonin will eventually lose its action site inthe kidney because no more phosphate will be excreted from glomeruli. Atsuch a disease stage, a potential value exists in controlling phosphateabsorption from the diet in the digestive tract. The digestive tract,particularly the intestine, is the only place where phosphate is takenup from the diet into the circulation. Therefore, this will be the nextmajor target to control phosphate uptake into the circulation after thekidney function is lost.

A subtype of the Type II NaPi, named Type lib was reported to be clonedfrom mouse intestine (Hilfiker, PNAS 95 (1998), 14564-14569). Althoughit is yet to be known if phosphatonin can effect on the intestinal TypeMb NaPi, it is reasonably expected that this Type lib NaPi in theintestine plays a major role in the absorption of phosphate from thediet and that phosphatonin may be the most significant factor for itsup- and downregulation.

EXAMPLE 7

Pharmaceutical Compositions

Pharmaceutical compositions may be formulated comprising a polypeptideaccording to the present invention optionally incorporating apharmaceutically-acceptable excipient, diluent or carrier. The exactnature and quantities of the components of such compositions may bedetermined empirically and will depend in part upon the route ofadministration of the composition. Routes of administration to patientsinclude oral, buccal, sublingual, topical (including ophthalmic),rectal, vaginal, nasal and parenteral (including intravenous,intraarterial, intramuscular, subcutaneous and intraarticular). In orderto avoid unwanted proteolysis, a parenteral route is preferred.

Suitable dosages of a molecule of the present invention will vary,depending upon factors such as the disease or disorder to be treated,the route of administration and the age and weight of the individual tobe treated. For instance for parenteral administration, a daily dosageof from 0.1 μg to 1.5 mg/kg of a molecule of the invention may besuitable for treating a typical adult. More suitably the dose might be 1μg to 150 μg. Accordingly, it is envisaged that the active polypeptideingredient may be given in a dose range of from 0.01 to 100 mg,typically 0.1 to 10 mg, on a daily basis for an adult human.

Compositions for parenteral administration for example will usuallycomprise a solution of the molecule dissolved in an acceptable carrier,preferably an aqueous carrier. A variety of aqueous carriers can be usedsuch as water, buffered water, 0.4% saline, 0.3% glycine etc. Suchsolutions should advantageously be sterile and generally free ofaggregate and other particulate matter. The compositions may containpharmaceutically acceptable buffers to adjust pH, or alter toxicity, forexample sodium acetate, sodium chloride, potassium chloride, calciumchloride, sodium lactate, etc. The concentration of molecule in theseformulations can vary widely, for example from less than about 0.5% toas much as 15 or 20% by weight and could be selected as appropriate by askilled person.

Typical pharmaceutical compositions are described in detail inRemington's Pharmaceutical Science, 15^(th) ed., Mack PublishingCompany, Easton, Pa. (1980). For example, pharmaceutical compositionsfor injection could be made up to contain 1 ml sterile buffered water,and 50 mg of molecule. A typical composition for infusion could be madeup to contain 250 ml of sterile Ringer's solution, and 150 mg ofmolecule. Actual methods for preparing compositions will be known orapparent to those skilled in the art. Approaches to formulation andadministration of polypeptide pharmaceutical compositions are well-knownto those skilled in this art and are discussed, for example, by P.Goddard in Advanced Drug Delivery Reviews, 6(1991) 103-131.

EXAMPLE 8

Further characterization of phosphatonin (MEPE) and its encoding gene

Clinical profile of patients (BD, ND, EM and PS) with oncocjenicosteomalacia:

Patient BD has been described in an earlier publication (Rowe, Bone 18(1996), 159-169), and a case report for patient ND has also beenpublished (David, J. Neurosug. 84 (1996), 288-292). Both patientsexhibited classical tumour-osteomalacia, and presented with low serumphosphate and radiological osteomalacia, and low serum 1,25 vitam D₃.Patient BD (44 year old woman), and patient ND (66 year old woman),exhibited complete remission of symptoms after removal of tumours fromthe left nasal cavity (haemangiopericytoma), and the intracranial space(mesenchymal hemopericytoma like tumour), respectively. Patient ND hadthree such operations over a period of twenty years, and remissionoccurred after each resection.

Tumour conditioned media:

Tumour samples from both BD, ND and EM were collected immediately afterresection. Samples were then cut into ˜1 mm pieces and some frozen inliquid nitrogen. The remaining pieces of tumour tissue were processedfor tissue culture as described previously (Rowe, Bone 18 (1996),159-169). In brief, samples were digested with collagenase overnight,and then subjected to alternate cycles of culture in the presence andabsence of serum (DMEM media). With patient ND, additional samples from,surrounding sub-dura, and dura were also collected and treated asdescribed above. Also, control skin fibroblast cultures from patient BDwere obtained on the same day as tumour resection, and treated in thesame way as the tumour samples. Samples from patient BD were labeled asfollows: 1: tumour conditioned media (TCM-BD); 2: skin conditioned media(SCM-BD). Samples from patient ND were labeled as follows: 1: Tumourconditioned media (TCM-ND); 2: sub-dura conditioned media (SDCM-ND); 3:dura conditioned media (DCM-ND); 4: fluid surroundingintracranial-tumour (FST-ND). All samples were collected from culturecycles in which cells were grown in serum-free DMEM media, unlessindicated in the text by addition of ‘serum supplemented’ to the aboveabbreviations.

Concanavilin A affinity chromatographv of TCM:

Concanavilin-A affinity chromatography of tumour conditioned medium(TCM) from patient ND, performed in accordance with Example 1 resultedin the isolation of high and low affinity fractions (HCA, and LCArespectively). Both HCA and LCA fractions were eluted withα-methyl-D-glucopyranoside (0.5M) elution buffer. Briefly, partialpurification of TCM proteins was carried out by Conacanavilin A affinitychromatography using a method described by (Wagner, Gen. Comp.Endocrinol. 63 (1986), 481-491), with modifications. Concanavilin ASepharose (Pharmacia Code No: 17-0440-01, 14 ml), in 20% Ethanol, wasfirst washed with several column volumes of water, and then equilibratedin running buffer (CRB: 0.06M Sodium phosphate pH 7.2 and 0.5M NaCI).The equilibrated slurry was then added to a 12 mm×115 mm Pharmacia screwtop column, and three column volumes of CRB running buffer added at aflow rate of 0.4 ml/min (FPLC/HPLC millenium Waters chromatographysystem). Conditioned media equilibrated in CRB buffer (10 ml), was thenadded to the column and allowed to bind. The column was then washed withseveral column volumes of CRB loading buffer, and elutions of boundproteins was then carried out by addition of sodium phosphate elutionbuffer (ERB; 60 mM pH 7.27/ 0.5M NaCI/0.5Mα-methyl-D-glucopyranoside/0.01% azide), at a flow rate of 0.2 ml/min(40 ml). High affinity proteins were eluted after incubation of thecolumn overnight in ERB buffer followed by a second passage of ERBbuffer at 0.2 ml/min. Elution profiles for both high and lowconcanavilin A-affinity TCM-proteins were identical and produced asingle symmetrical peak at ˜1.6 column volumes. Peak LCA represented ⅓the total mass of peak HCA, and 1 ug of HCA material was retrieved from10 ml of tumour conditioned media (TCM), from patient ND.

SDS-PAGE of TCM and concanavilin A fractions:

Tumour conditioned medium, conditioned media and concanavilin A peaks(HCA and LCA), were separated by SDS-PAGE and visualized afterSybr-Orange staining. SDS-polyacrylamide gel electrophoresis was carriedout using a Novex NuPAGE™ Electrophoresis system consisting of 4-12%Bis-Tris acrylamide-gradient gels (pH 6.4), and MOPS-SDS (50 mM3-[N-morpholino] propane sulfonic acid; 50 mM Tris-base; 3.5 mM SDS; 1.0mM EDTA; pH 7.7) running buffer. Runs were carried out at a constantvoltage of 200 for 50 min. Samples were denatured at 70° C. for 10minutes in NuPage LDS sample buffer (10% glycerol; 1.7% Tris-Base; 1.7%Tris-HCI; 2% Lithium Dodecyl Sulfate; dithiotnreitol 50 mM; 0.015% EDTA;0.075% Serva Blue G250; 0.025% Phenol red; pH7.5 final concentration).NuPage antioxidant was added to the upper electrophoresis chamber asrecommended by the manufacturers. Following electrophoresis proteinswere stained by incubating the gels in 7.5% acetic acid supplementedwith SYPRO-Orange. Visualization of proteins was achieved after UVillumination using a Bio-Rad Fluorlmager gel-imaging system. HCA and LCAfractions stained positive for two proteins at 56 kDa and 200 kDarespectively and gave identical profiles. Conditioned media (patientND), from intracranial-tumour, sub-dura (immediately adjacent to tumourin the patient), and dura material contained several major bandsspanning ˜50-80 kDa. A prominent band was present in all preparations at˜66 kDa with a weaker very high molecular weight component at ˜200 kDapresent in tumour and sub-dura. The relative intensity of the ˜200 kDawas highest in the tumour material, and absent in the dura. A diffuseset of bands at ˜55-60 kDa was present in tumour and sub-dura but absentin the dura conditioned media (patient ND). Conditioned media from skinand media control did not reveal any staining for protein. Conditionedmedia from patient BD and EM gave similar profiles except for theabsence of the high molecular weight protein at 200 kDa.

Non phosphaturic tumour tissues from patients LA and SL, and also skincontrols all contained the 66 kDa band and also diffuse staining at50-60 kDa. Concanavilin-A affinity peaks HCA and LCA were enriched forthe high molecular weight 200 kDa band and also contained proteins fromthe 50-66 kDa range. Conditioned media from bone cell lines HTB96 andSaOs2 gave almost identical protein profiles to tumour conditioned mediafrom OHO-patient ND. The 200 kDa band intensity in SaOS2 was reducedrelative to TCM from brain tumour (patient ND), sub-dura (patient ND),and CM from HTB96.

Immuno-blottina and glvcoprotein staining of TCM and purified fractions:

For western-blotting, proteins were transferred to PVDF membranes(Amersham), using submarine electrophoresis. After SDS-PAGEelectrophoresis, gels were equilibrated in transfer buffer: 25 mMTris-HCI; 0.38 M glycine; 0.2% SDS (TB) for 1 h at room temperature.PVDF membranes were cut to size, briefly rinsed in methanol, washed indistilled water, and then equilibrated in TB. The equilibrated gel andPVDF membrane were then sandwiched between filters and placed in acassette. The cassette was then placed in a Hoeffer system submarineelectroblotter with TB buffer and cooling maintained at 4° C. bythermocooler. Transfer of proteins was then carried out by positioningthe PVDF end of the sandwich towards the anode, and electrophoresis at aconstant 0.4 A (45V), for 45 min. Blots were screened with 1/1000dilution of pre-Anti-op antisera, post-Anti-op-antisera, or calmodulinconjugated to alkaline phosphatase using the methods described in theEnhanced-Chemiluminescence kit (Amersham; ECL+), or the calmodulinaffinity detection kit (Stratagene) respectively. Chemiluminescence, wasdetected and filmed using the Bio-Rad Fiuorlmaging system, and thecalmodulin-affinity binding was visualized using the colourometricsystem discussed earlier for clone detection (Stratagene). Biotinylatedmolecular weight markers (Amersham), were used as internal controls toasses transfer and molecular weight. Streptavidin conjugated to horseradish peroxidase (HRP), was added to the secondary antibody(goat-anti-rabbit IgG conjugated to HRP), to facilitate visualization ofthe biotinylated-markers via Chemiluminescence. Western blots ofphosphaturic tumour-conditioned-media (TCM), from OHO-patients gavepositive chemiluminescent bands when screened with pre-absorbedpre-operation antisera. Non-phosphaturic tumours, tissue controls fromskin and media controls were all negative when screened withpre-absorbed pre-operation antisera. Also, all TCM and conditioned mediasamples were negative when screened with post-operation antisera.

Screening of TCM proteins from patient ND, and osteosarcoma cell linesHTB96 and SaOS2 with pre-absorbed pre-operation antiserum revealed twodistinct immuno-positive bands at ˜54-57 kDa and ˜200 kDa. Patient NDtumour sample and adjacent sub-dura tissue gave much stronger 54-57 kDasignals relative to dura brain-sample conditioned-media, and no stainingfor the 200 kDa band was found in the dura conditioned-media. Both HCAand LCA concanavilin-A fractions contained a very strong signal for the200 kDa band, and a reduced but visible signal at 54-57 kDa. Cell linesSaOS2 and HTB96 were also positive for the same bands, but SaOS2conditioned media had a reduced signal for the 200 kDa band relative toTCM and HTB96.

Skin conditioned media (patient ND and BD), and media controls werenegative, as were screenings with post-operation antisera (Rowe, Bone 18(1996), 159-169). Recombinant MERE (rec-MEPE), stained positively withpre-absorbed pre-operation antisera, and this could be competed out withadded rec-MEPE). A positive band of 54-57 kDa was obtained withSybr-Orange protein stained, and pre-absorbed pre-operation antiserascreened rec-MEPE. This was the same size as the 55-57 kDa band(pre-absorbed-pre-operation western screened), found with patient NDtumour conditioned media, and osteosarcoma cell lines HTB96 and SaOS2.Recombinant-MEPE contains an additional 4.5 kDa CBP-tag at theN-terminus that decreases mobility and results in an apparent increasein molecular weight on SDS-PAGE gels. Thus, the equivalent size oftumour derived protein and rec-MEPE may be due to post-translationalmodification of tumour derived MEPE (possibly glycosylation).

TCM western blots from OHO-tumour patients BD and EM contained majorpre-absorbed-pre-operation antisera positive bands at slightly lowermolecular weight (48-52 kDa), as well as a band co-migrating at 55-57kDa with rec-MEPE. Other higher molecular weight bands were also seen at61, 75, 80, and 93 kDa (weaker signals).

In all samples the major SYBR-Orange stained protein band at 66 kDa wasnegative when screened with pre-absorbed pre-operation antisera.Glycoprotein screening of duplicate blots gave the same results asscreening with pre-operation antisera and both 54-57 kDa and 200 kDabands stained positive confirming that these proteins are glycosylated.Proteins were separated by SDS-PAGE and blotted onto PVDF membranes asdescribed in methods above. Specific glycoprotein detection was carriedout using an Immuno-Blot kit for glycoprotein detection (Bio-Rad), andAmersham biotinylated markers were added as internal controls. Briefly,after transfer membranes were treated with 10 mM sodium periodate insodium acetate/EDTA buffer to oxidise carbohydrate moieties. The blotswere then washed in PBS and incubated with hydrazide insodtum/acetate/EDTA buffer for 60 minutes at room temperature. Filterswere then washed three times (10 minutes) with IBS. Subsequent blockingand detection was carried out as described earlier using the Enhancedchemiluminescence kit (Amersham), and streptavidin horse radishperoxidase. Primary antibody and secondary goat anti-rabbit-HRP was notused.

In conclusion pre-absorbed pre-operation antisera specifically detectsproteins derived from oncogenic hypophosphatemic osteomalacia-TCM. Themajor proteins detected fall into two three distinct molecular sizeranges 48-52 kDa, 54-57 kDa, and 200 kDa, All OHO-TCM samples werepositive for the 54-57 kDa protein, and all proteins detected bypre-absorbed-pre-operation antisera stained positive when screened forglycoprotein status. Non OHO-tumours control tissues and media werenegative when screened with pre-absorbed pre-operation antisera.

EXAMPLE 9

Expression of MERE fusion-protein from pCAL-n-EK vector

The entire cDNA coding sequence was subcloned into pCAL-n-EK asdescribed in Example 4a. Validation of the fusion construct generated byIPTG induction of the E. coli host BL21 (DE3), was achieved by screeningwestern blots with pre-operation antisera, and also with calmodulinconjugated to alkaline phosphatase as described above. The fusionprotein with microbial CBP-tag (calmodulin binding peptide of 4.5 kDa),containing calmodulin peptide, enterokinase site, and thrombin site was56 kDa as deduced by SDS-PAGE. This is in approximate agreement with theexpected molecular size (˜48 kDa). Purification of protein was achievedby calmodulin affinity chromatography as described above. Preincubationof pre-operation antisera with purified fusion construct resulted in adiminution of the 55-57 kDa signal observed on screening TCM westernblots, but not the 200 kDa band. The failure to completely reduce the55-57 kDa signal was presumed to be due to specific recognition of thehighly antigenic glycosylation moiety present in the nascentMEPE-protein (TCM), but absent in the microbial fusion-construct ofrec-MEPE. The fusion protein was soluble in aqueous Tris-buffers anddetergents were not required at any stage of the purification process.

EXAMPLE 10

Tissue expression (RT/PCR and Northern analysis)

Northern blots containing poly A+RNA were screened with MEPE cDNA and nohybridization was detected to stomach, thyroid, spinal cord, lymph node,trachea, adrenal gland, bone marrow, heart, brain, lung, liver, skeletalmuscle, kidney, and pancreas (Clontech MTN-blots I and III). ForNorthern analysis two blots from Clontech (MTN™ and MTN™III), containingthe following poly A⁺ RNA's: 1; heart, 2; brain, 3; placenta, 4; lung,5; liver, 6; skeletal muscle, 7; kidney, 8; pancreas, 9; stomach, 10;thyroid, 11; spinal cord, 12; lymph node, 13; trachea, 14; adrenalgland, 15; bone marrow, were screened with MEPE cDNA amplified withspecific internal primers (Pho433-111F and PHO877-111R). Primersequences for Pho433-111F and PHO877-111R are highlighted in FIG. 8(nucleotide positions 433 to 456 (SEQ ID NO: 24) and 877 to 900 (SEQ IDNO: 25), respectively), and the following PCR conditions were used:predenaturation; 95° C . 3 min; followed by thirty cycles ofdenaturation; 95° C. 45 sec, annealing; 65° C. 30 sec, polymerization;72° C. 45 sec, and a final extension of 72° C. 7 min followed by coolingto 4° C. PCR-buffer (PB), was used with a final concentration of 2 mMMgCl₂. The 444 bp amplified MEPE cDNA product was then resolved bysubmarine agarose electrophoresis, visualized by ethidium bromidestaining, and purified using glass beads (Gene-clean II kit; Bio 101INC). Purified DNA was then radiolabeled using α-P³² dCTP (3000 ci/mmol)in conjunction with the MegaPrime labeling-kit from Amersham. Specificactivities of 5×10⁹ cpm/μg were routinely obtained. Hybridization (60°C.), and prehybridization (60° C.), of blots were carried out usingpublished methods (Rowe, Hum. Genet. 97 (1996), 354-352), and stringencywashes were carried out as follows: 1; two washes at room temperaturefor 30 min with 2×SSC 0.1%SDS, two washes at 60° C. for 30 min in0.1×SSC 0.1% SDS. Filters were then exposed to film for 7 days at −80Cand the films developed. Total human-RNA from adrenal glands, brain,duodenum, heart, kidney, liver, lung, skin, spleen, thymus, thyroid,tonsil, did not amplify using RT/PCR and MEPE specific primers, althoughevidence for low level expression using cDNA template was found forbrain, kidney, liver and pancreas. For this experiment, total RNA wasextracted from the following human tissues: 1; Thymus, 2; brain, 3;testis, 4; duodenum, 5; heart, 6; skin, 7; liver, 8; tonsil, 9; spleen,10; thyroid, 11; adrenal, 12; lung, 13; kidney, 14; OHO-tumour tissue,14; Human primary osteoblast. Total RNA from Rat primary osteoblast wasalso obtained. MEPE Internal primers as described above (Pho433-111F andPHO877-111R), were used to copy total RNA using reversetranscriptase-PCR and the Perkin Elmer-Roche RNA PCR kit. Briefly, 1 ugof total RNA was dissolved in 20 μl of 10 mM Tris-HCl (pH 8.3), 50 mMKCl, 5 mM MgCl₂, 1 mM dNTPs, 1 unit/l ribonuclease inhibitor, 2.5unit/μl MULV reverse transcriptase, 0.75 μM down stream primer(PHO877-111R). The mixture was then incubated at 37° C. for 10 min.Upstream primer (Pho433-111F), dNTPs, MgCl₂, and AmpliTaq DNApolymerase, was then added to give final concentrations of 0.15 μM, 200μM, 2 mM, and 2.5 units/100 μl respectively in a total volume of 100 μl.PCR was then carried out using a Perkin Elmer thermocycler (system9700), set to the following program: predenaturation; 95° C. 3 min;followed by thirty five cycles of denaturation; 95° C. 45 sec,annealing; 65° C. 30 sec, polymerization; 72° C. 45 sec, and a finalextension of 72° C. 7 min followed by cooling to 4° C. Amplifiedproducts were resolved using agarose-gel electrophoresis, and verifiedby southern blotting, and sequencing. Also, a panel of normalized cDNA'sderived from a range of non-OHO tumours (Breast carcinoma, lungcarcinoma I, colon adenocarcinoma I, lung carcinoma II, prostaticadenocarcinoma, colon adenocarcinoma II, ovarian carcinoma, pancreaticcarcinoma; Clontech human-tumour panel #K1422-1) were all negative toMERE PCR, except for very low level expression in one case of colonadenocarcinoma, ovarian carcinoma, and prostatic carcinoma respectively(detected after southern screening of RT/PCR amplified products withradiolabeled MEPE cDNA). In sharp contrast, RT/PCR using MEPE primersamplified poly A+ RNA, from OHO tumours, from four separate patients BD,DM, EM, and DS, indicating high levels of expression (normalized againstglyceraldehyde 3-phosphate dehydrogenase and transferring Poly A+RNAfrom non-phosphaturic tumours and control tissues from OHO-patients(skin and material adjacent to tumours), CL8 human-renal cell line,human primary osteoblast cells (purchased from Clonetics H-OST, seematerials), and poly A+RNA extracted from a presumed tumour-polyp from apatient with linear sebaceous naevus syndrome (TCM from polyp did notinhibit phosphate uptake in human renal cell line CL8), did not amplifyusing MEPE specific primers. Using Clontech purchased cDNA's derivedfrom heart, brain, placenta, lung, liver, skeletal muscle, kidney, andpancreas (human panel I #K1420-1), as templates for MEPE primer PCR, lowlevel expression was detected in brain, liver, lung and pancreas.Sequencing of the MEPE-primer amplified bands revealed complete homologyto MEPE cDNA and southern screening of the amplified bands with MEPEcDNA confirmed the sequencing results. OHO template poly A+ RNA from allOHO-patients consistently amplified an expected band of 480 bp and alower band of 190 bp. The upper band was confirmed by sequencing andsouthern autoradiography as completely homologous to MEPE sequence, andthe lower band was confirmed as a MEPE-derivative by southern analysis.The lower band did not appear in the low level expression normal-tissuesor non OHO-tumours. This indicates that alternative splicing may play arole in the tumour derived MEPE. All RT/PCR and PCR experiments werenormalized against G3PDH and transferrin.

In summary high level expression of MEPE (as measured by mRNA levels),was found only in OHO-tumour samples, and evidence for very low levelexpression (possibly ectopic), was found in brain, liver, kidney andthree out of eleven non-OHO tumours. Eight out of eleven tumours werenegative for MEPE mRNA expression (RT/PCR), and all results werestandardized against GA3PDH and transferrin RT/PCR primers,

EXAMPLE 11

Southern analysis (Genomic blots)

Genomic blots containing immobilized DMA derived from a family withautosomal rickets (Rowe, Hum. Genet. 91 (1993), 571-575), and digestedwith Pstl, EcoRI, Pvull, and Mspl respectively were screened withradiolabeled MEPE cDNA as described above. Southern analysis was carriedout using genomic digests of DNA extracted from blood as describedpreviously (Rowe, Hum. Genet. 93 (1994), 291-294). The Pstl blotrevealed the presence of an 11 kb band and also a 4 kb polymorphism inone of the sixteen family members screened. The EcoRI, Pvull, and Msplblots were all positive for single bands of 6 kb, 6.5 kb, and 4 kbrespectively, and confirmed the human provenance of the gene. Due to thelack of genetic information it was not possible to deduce whether thegene segregated with the disease in this autosomal rickets family.

EXAMPLE 12

Phosphate uptake in a human renal cell line CL8: TCM and MEPEsupplementation

Phosphate and glucose uptake experiments were conducted on a human renalcell line (CL8) as described previously (Rowe, Bone 18 (1996), 159-169).In brief cells were cultured in defined medium (DM), to confluency orovernight incubation in 24 well flat bottom tissue culture plates(Falcon 3047). The DM was then replaced with fresh DM supplemented withpurified fusion protein or concanavilin affinity purified TCM and leftovernight at 37° C. Uptake of P³² and C¹⁴ methyl-glucose was thenmeasured (Rowe, Bone 18 (1996), 159-169).

Addition of TCM (1/20 dilution), to human renal cell lines resulted in asignificant reduction in Na+ dependent phosphate uptake as reportedearlier (Rowe, Bone 18 (1996), 159-169). This inhibition was preventedby preincubation of TCM with pre-operation and not post operationantisera, also reported earlier (Rowe, Bone 18 (1996), 159-169).Addition of high and low affinity concanavilin-A purified fractions (HCAand LCA respectively), at concentrations of 40 ng/ml also resulted ininhibition of Na+ dependent phosphate uptake (NaPi). In both TCM andconcanavilin-A fractions the inhibition was specific to phosphateuptake, and did not affect of Na+ dependent a-methyl-D-glucose uptake.In all cases the affects were dose dependent.

Similar experiments were carried out with MEPE fusion-protein purifiedby calmodulin affinity chromatography. Surprisingly, recombinant MEPEdid not inhibit Na+ dependent phosphate co-transport, but increasedphosphate uptake in a dose dependent manner (see FIG. 24). A doubling ofphosphate uptake was observed at 1000 ng/ml (p<0.001). These experimentsconfirm that MEPE fusion protein specifically increases Na+ dependentphosphate co-transport in a human renal cell line CL8.

While the present invention has been described with reference to thespecific embodiments it should be understood by those skilled in the artthat various changes may be made and equivalents may be substitutedwithout departing from the true scope and spirit of the invention. Inaddition, many modifications may be made to adapt to a particularsituation, material, composition of matter, process step or steps, tothe objective, spirit or scope of the present invention. All suchmodifications are intended to be within the scope of the claims appendedhereto.

The entire disclosure of each document cited (including patents, patentapplications, journal articles, abstracts, laboratory manuals, books, orother disclosures) in the Background of the Invention, DetailedDescription, and Examples is hereby incorporated herein by reference.Moreover, the sequence listing is herein incorporated by reference.

1-41. (Canceled)
 42. A method of treatment, comprising the steps of:administering to a patient a therapeutically effective amount of aformulation comprising a carrier and a polypeptide having phosphatoninactivity; and allowing the formulation to effect phosphate metabolism inthe patient.
 43. The method of claim 42, wherein the polypeptide has amolecular weight in the range of from about 53 to 60 kDa as measured bySDS-PAGE.
 44. The method If claim 42, wherein the polypeptide has amolecular weight of about 200 kDa as measured by bis-tris SDS-PAGE at pH7.
 45. The method of claim 42, wherein the polypeptide comprises SEQ IDNO:2.
 46. The method of claim 42, wherein the polypeptide isglycosylated.
 47. The method of claim 42, wherein the polypeptide isphosphorylated.
 48. The method of claim 42, wherein the polypeptide isphosphorylated and glycosylated.
 49. The method of claim 42, whereinsaid polypeptide has an amino acid sequence that is at least 90%identical to the contiguous amino acid sequence set forth in SEQ IDNO:2.
 50. An isolated polypeptide having phosphatonin activity whichpolypeptide is glycosylated.
 51. The polypeptide of claim 50 whichpolypeptide is phosphorylated.
 52. An isolated polypeptide havingphosphatonin activity which polypeptide is phosphorylated.
 53. Thepolypeptide of claim 50, comprising SEQ ID NO:2.
 54. The polypeptide ofclaim 50, encoded by a polynucleotide sequence chosen from apolynucleotide sequence comprising SEQ ID NO: 1 and a polynucleotidesequence which hybridizes to SEQ ID NO: 1 under stringent hybridizationconditions and wherein the polypeptide has phosphatonin activity.
 55. Anisolated polypeptide comprising a fragment of SEQ ID NO:2 chosen fromamino acid residues 1 to 40, 141 to 180 and 401 to
 429. 56. An isolatedpolypeptide comprising a fragment of SEQ ID NO:2 wherein the fragmenthas phosphatonin activity.
 57. The polypeptide of claim 56, wherein thefragment is chosen from fragments 20-30, 100-130, 145-160, 300-310,320-340 and 380-430 of SEQ ID NO:2.
 58. The polypeptide of claim 56,wherein the fragment is a C-terminal fragment.
 59. The polypeptide ofclaim 56, wherein the fragment is an N-terminal fragment.